< draft-ietf-oauth-signed-http-request-01.txt   draft-ietf-oauth-signed-http-request-02.txt >
OAuth Working Group J. Richer, Ed. OAuth Working Group J. Richer, Ed.
Internet-Draft Internet-Draft
Intended status: Experimental J. Bradley Intended status: Standards Track J. Bradley
Expires: September 10, 2015 Ping Identity Expires: August 6, 2016 Ping Identity
H. Tschofenig H. Tschofenig
ARM Limited ARM Limited
March 09, 2015 February 03, 2016
A Method for Signing an HTTP Requests for OAuth A Method for Signing HTTP Requests for OAuth
draft-ietf-oauth-signed-http-request-01.txt draft-ietf-oauth-signed-http-request-02
Abstract Abstract
This document a method for offering data origin authentication and This document a method for offering data origin authentication and
integrity protection of HTTP requests. To convey the relevant data integrity protection of HTTP requests. To convey the relevant data
items in the request a JSON-based encapsulation is used and the JSON items in the request a JSON-based encapsulation is used and the JSON
Web Signature (JWS) technique is re-used. JWS offers integrity Web Signature (JWS) technique is re-used. JWS offers integrity
protection using symmetric as well as asymmetric cryptography. protection using symmetric as well as asymmetric cryptography.
Status of This Memo Status of This Memo
skipping to change at page 1, line 37 skipping to change at page 1, line 37
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on September 10, 2015. This Internet-Draft will expire on August 6, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Generating a JSON Object from an HTTP Request . . . . . . . . 3 3. Generating a JSON Object from an HTTP Request . . . . . . . . 3
3.1. Selection of a hashing algorithm and size . . . . . . . . 4 3.1. Calculating the query parameter list and hash . . . . . . 4
3.2. Calculating the query parameter list and hash . . . . . . 4 3.2. Calculating the header list and hash . . . . . . . . . . 5
3.3. Calculating the header list and hash . . . . . . . . . . 5 4. Sending the signed object . . . . . . . . . . . . . . . . . . 6
4. Verifying the Hashes . . . . . . . . . . . . . . . . . . . . 5 4.1. HTTP Authorization header . . . . . . . . . . . . . . . . 6
4.1. Validating the query parameter list and hash . . . . . . 6 4.2. HTTP Form body . . . . . . . . . . . . . . . . . . . . . 6
4.2. Validating the header list and hash . . . . . . . . . . . 6 4.3. HTTP Query parameter . . . . . . . . . . . . . . . . . . 6
5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. Validating the request . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5.1. Validating the query parameter list and hash . . . . . . 7
6.1. The 'pop' OAuth Access Token Type . . . . . . . . . . . . 7 5.2. Validating the header list and hash . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6.1. The 'pop' OAuth Access Token Type . . . . . . . . . . . . 8
6.2. JSON Web Signature and Encryption Type Values 6.2. JSON Web Signature and Encryption Type Values
Registration . . . . . . . . . . . . . . . . . . . . . . 8 Registration . . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7.1. Offering Confidentiality Protection for Access to 7.1. Offering Confidentiality Protection for Access to
Protected Resources . . . . . . . . . . . . . . . . 8 Protected Resources . . . . . . . . . . . . . . . . 9
7.2. Authentication of Resource Servers . . . . . . . . . . . 8 7.2. Plaintext Storage of Credentials . . . . . . . . . . . . 9
7.3. Plaintext Storage of Credentials . . . . . . . . . . . . 9 7.3. Entropy of Keys . . . . . . . . . . . . . . . . . . . . . 10
7.4. Entropy of Keys . . . . . . . . . . . . . . . . . . . . . 9 7.4. Denial of Service . . . . . . . . . . . . . . . . . . . . 10
7.5. Denial of Service . . . . . . . . . . . . . . . . . . . . 9 7.5. Validating the integrity of HTTP Headers and Query
7.6. Protecting HTTP Header Fields . . . . . . . . . . . . . . 10 Parameters . . . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 10 10. Normative References . . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction 1. Introduction
In order to protect an HTTP request with a signature, a method for In order to prove possession of an access token and its associated
conveying various parameters and to compute a signature is needed. key, an OAuth 2.0 client needs to compute some cryptographic function
Ideally, this should be done without replicating the information and present the results to the protected resource as a signature.
already present in the HTTP request. This version of the document The protected resource then needs to verify the signature and compare
still replicates most of the headers though. that to the expected keys associated with the access token. This is
in addition to the normal token protections provided by a bearer
The keying material required for this signature calculation is token [RFC6750] and transport layer security (TLS).
distributed via mechanisms described in companion documents (see
[I-D.bradley-oauth-pop-key-distribution] and
[I-D.hunt-oauth-pop-architecture]). The JSON Web Signature (JWS)
specification [I-D.ietf-jose-json-web-signature] is re-used for
computing a digital signature (which uses asymmetric cryptography) or
a keyed message digest (in case of symmetric cryptography).
The scope of the mechanism described in this document is shown in
Figure 1 where a client in possession of keying material that is tied
to the access token creates a JSON object, signs it, and issues an
request to a resource server for access to a protected resource.
+-----------+ +------------+
| |--(1)- HTTP Request ->| Resource |
| Client | (+Signature, +Access Token)->| Server |
| | | |
| |<-(2)- HTTP Response ---------------| |
+-----------+ +------------+
Figure 1: Message Flow. Furthermore, it is desirable to bind the signature to the HTTP
request. Ideally, this should be done without replicating the
information already present in the HTTP request more than required.
Many HTTP application frameworks insert extra headers, query However, many HTTP application frameworks insert extra headers, query
parameters, and otherwise manipulate the HTTP request on its way from parameters, and otherwise manipulate the HTTP request on its way from
the web server into the application code itself. It is the goal of the web server into the application code itself. It is the goal of
this draft to have a signature protection mechanism that is this draft to have a signature protection mechanism that is
sufficiently robust against such deployment constraints (while still sufficiently robust against such deployment constraints while still
providing sufficient security benefits). providing sufficient security benefits.
The method of conveying the token and signed request to the protected The key required for this signature calculation is distributed via
resource server is undefined by this document, but [RFC6750] could be mechanisms described in companion documents (see
re-used. [I-D.ietf-oauth-pop-key-distribution] and
[I-D.ietf-oauth-pop-architecture]). The JSON Web Signature (JWS)
specification [RFC7515] is used for computing a digital signature
(which uses asymmetric cryptography) or a keyed message digest (in
case of symmetric cryptography).
The mechanism described in this document does not provide The mechanism described in this document assumes that a client is in
authentication of the resource server to the client. This version of possession of an access token and asociated key. That client then
the document does not provide a cryptographic binding to Transport creates a JSON object including the access token, signs the JSON
Layer Security (TLS) used underneath the an HTTPS request. object using JWS, and issues an request to a resource server for
access to a protected resource using the signed object as its
authorization.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119].
Other terms such as "client", "authorization server", "access token",
and "protected resource" are inherited from OAuth 2.0 [RFC6749].
We use the term 'sign' (or 'signature') to denote both a keyed We use the term 'sign' (or 'signature') to denote both a keyed
message digest and a digital signature operation. message digest and a digital signature operation.
3. Generating a JSON Object from an HTTP Request 3. Generating a JSON Object from an HTTP Request
This section describes how to generate a JSON object below is This specification uses JSON Web Signatures [RFC7515] to protect the
included as a member of the JSON object. All members are OPTIONAL. access token and, optionally, parts of the request.
m The HTTP Method used to make this request. This MUST be the This section describes how to generate a JSON [RFC7159] object from
uppercase HTTP verb as a JSON string. the HTTP request. Each value below is included as a member of the
JSON object at the top level.
u The HTTP URL host component as a JSON string. This MAY include at REQUIRED. The access token value. This string is assumed to have
the port separated from the host by a colon in host:port format. no particular format or structure and remains opaque to the
client.
p The HTTP URL path component of the request as an HTTP string. ts RECOMMENDED. The timestamp. This integer provides replay
protection of the signed JSON object. Its value MUST be a number
containing an integer value representing number of whole integer
seconds from midnight, January 1, 1970 GMT.
q The hashed HTTP URL query parameter map of the request as a two- m OPTIONAL. The HTTP Method used to make this request. This MUST
part JSON array. The first part of this array is a JSON array be the uppercase HTTP verb as a JSON string.
listing all query parameters that were used in the calculation of
the hash in the order that they were added to the hashed value as
described below. The second part of this array is a JSON string
containing the Base64URL encoded hash itself, calculated as
described below.
h The hashed HTTP request headers as a two-part JSON array. The u OPTIONAL. The HTTP URL host component as a JSON string. This MAY
first part of this array is a JSON array listing all headers that include the port separated from the host by a colon in host:port
were used in the calculation of the hash in the order that they format.
were added to the hashed value as described below. The second
part of this array is a JSON string containing the Base64URL
encoded hash itself, calculated as described below.
b The base64URL encoded hash of the HTTP Request body, calculated as p OPTIONAL. The HTTP URL path component of the request as an HTTP
the HMAC of the byte array of the body. string.
ts The "ts" (timestamp) element provides replay protection of the q OPTIONAL. The hashed HTTP URL query parameter map of the request
JSON object. Its value MUST be a number containing an IntDate as a two-part JSON array. The first part of this array is a JSON
value representing number of whole integer seconds from midnight, array listing all query parameters that were used in the
January 1, 1970 GMT. calculation of the hash in the order that they were added to the
hashed value as described below. The second part of this array is
a JSON string containing the Base64URL encoded hash itself,
calculated as described below.
3.1. Selection of a hashing algorithm and size h OPTIONAL. The hashed HTTP request headers as a two-part JSON
array. The first part of this array is a JSON array listing all
headers that were used in the calculation of the hash in the order
that they were added to the hashed value as described below. The
second part of this array is a JSON string containing the
Base64URL encoded hash itself, calculated as described below.
The hashes SHALL be calculated using the HMAC algorithm using a hash b OPTIONAL. The base64URL encoded hash of the HTTP Request body,
size equal to the size of the surrounding JWT's alg header field. calculated as the SHA256 of the byte array of the body
That is, if the JWT uses HS256 or RS256, the HMAC here uses a 256-bit
HMAC. If the JWT uses RS512, the HMAC here uses 512-bit HMAC, and so
forth.
3.2. Calculating the query parameter list and hash All hashes SHALL be calculated using the SHA256 algorithm. [[ Note to
WG: do we want crypto agility here? If so how do we signal this ]]
The JSON object is signed using the algorithm appropriate to the
associated access token key, usually communicated as part of key
distribution [I-D.ietf-oauth-pop-key-distribution].
3.1. Calculating the query parameter list and hash
To generate the query parameter list and hash, the client creates two To generate the query parameter list and hash, the client creates two
data objects: an ordered list of strings to hold the query parameter data objects: an ordered list of strings to hold the query parameter
names and a string buffer to hold the data to be hashed. names and a string buffer to hold the data to be hashed.
The client iterates through all query parameters in whatever order it The client iterates through all query parameters in whatever order it
chooses and for each query parameter it does the following: chooses and for each query parameter it does the following:
1. Adds the name of the query parameter to the end of the list. 1. Adds the name of the query parameter to the end of the list.
2. Encodes the name and value of the query parameter as "name=value" 2. Encodes the name and value of the query parameter as "name=value"
and appends it to the string buffer. [[Separated by an and appends it to the string buffer separated by the ampersand
ampersand? Alternatively we could have this also pulled into an "&" character.
ordered list and post-process the concatenation, but that might
be too deep into the weeds. ]]
Repeated parameter names are processed separately with no special Repeated parameter names are processed separately with no special
handling. Parameters MAY be skipped by the client if they are not handling. Parameters MAY be skipped by the client if they are not
required (or desired) to be covered by the signature. required (or desired) to be covered by the signature.
The client then calculates the HMAC hash over the resulting string The client then calculates the hash over the resulting string buffer.
buffer. The list and the hash result are added as the value of the The list and the hash result are added to a list as the value of the
"p" member. "p" member.
3.3. Calculating the header list and hash For example, the query parameter set of "b=bar", "a=foo", "c=duck" is
concatenated into the string:
b=bar&a=foo&c=duck
When added to the JSON structure using this process, the results are:
"p": [["b", "a", "c"], "u4LgkGUWhP9MsKrEjA4dizIllDXluDku6ZqCeyuR-JY"]
3.2. Calculating the header list and hash
To generate the header list and hash, the client creates two data To generate the header list and hash, the client creates two data
objects: an ordered list of strings to hold the header names and a objects: an ordered list of strings to hold the header names and a
string buffer to hold the data to be hashed. string buffer to hold the data to be hashed.
The client iterates through all query parameters in whatever order it The client iterates through all query parameters in whatever order it
chooses and for each query parameter it does the following: chooses and for each query parameter it does the following:
1. Adds the name of the header to the end of the list. 1. Lowercases the header name.
2. Encodes the name and value of the header as "name: value" and 2. Adds the name of the header to the end of the list.
appends it to the string buffer. [[Separated by a newline?
Alternatively we could have this also pulled into an ordered list 3. Encodes the name and value of the header as "name: value" and
and post-process the concatenation, but that might be too deep appends it to the string buffer separated by a newline "\n"
into the weeds. ]] character.
Repeated header names are processed separately with no special Repeated header names are processed separately with no special
handling. Headers MAY be skipped by the client if they are not handling. Headers MAY be skipped by the client if they are not
required (or desired) to be covered by the signature. required (or desired) to be covered by the signature.
The client then calculates the HMAC hash over the resulting string The client then calculates the hash over the resulting string buffer.
buffer. The list and the hash result are added as the value of the The list and the hash result are added to a list as the value of the
"h" member. "h" member.
4. Verifying the Hashes For example, the headers "Content-Type: application/json" and "Etag:
742-3u8f34-3r2nvv3" are concatenated into the string:
Validation of the overall signature is done using the standard JWS content-type: application/json
mechanisms for JSON structures. However, in order to trust any of etag: 742-3u8f34-3r2nvv3
the hashed mechanisms above, an application MUST re-create and verify
a hash for each component. Additionally, an application MUST compare
the replicated values included in various JSON fields with the actual
header fields of the request. Failure to-do so will allow an
attacker to modify the underlying request, connect do different
resources while at the same time having the application layer verify
the signature correctly.
4.1. Validating the query parameter list and hash "h": [["content-type", "etag"], "bZA981YJBrPlIzOvplbu3e7ueREXXr38vSkxIBYOaxI"]
4. Sending the signed object
In order to send the signed object to the protected resource, the
client includes it in one of the following three places.
4.1. HTTP Authorization header
The client SHOULD send the signed object to the protected resource in
the Authorization header. The value of the signed object in JWS
compact form is appended to the Authorization header as a PoP value.
This is the preferred method. Note that if this method is used, the
Authorization header MUST NOT be included in the protected elements
of the signed object.
GET /resource/foo
Authorization: PoP eyJ....
4.2. HTTP Form body
If the client is sending the request as a form-encoded HTTP message
with parameters in the body, the client MAY send the signed object as
part of that form body. The value of the signed object in JWS
compact form is sent as the form parameter pop_access_token. Note
that if this method is used, the body hash cannot be included in the
protected elements of the signed object.
POST /resource
Content-type: application/www-form-encoded
pop_access_token=eyJ....
4.3. HTTP Query parameter
If neither the Authorization header nor the form-encoded body
parameter are available to the client, the client MAY send the signed
object as a query parameter. The value of the signed object in JWS
compact form is sent as the query parameter pop_access_token. Note
that if this method is used, the pop_access_token parameter MUST NOT
be included in the protected elements of the signed object.
GET /resource?pop_access_token=eyJ....
5. Validating the request
Just like with a bearer token [RFC6750], while the access token value
included in the signed object is opaque to the client, it MUST be
understood by the protected resource in order to fulfill the request.
Also like a bearer token, the protected resource traditionally has
several methods at its disposal for understanding the access token.
It can look up the token locally (such as in a database), it can
parse a structured token (such as JWT [RFC7519]), or it can use a
service to look up token information (such as introspection
[RFC7662]). However token information is looked up, the protected
resource MUST have access to the key associated with the access
token, which is required to validate the signature of the incoming
request. Validation of the signature is done using normal JWS
validation for the signature and key type.
Additionally, in order to trust any of the hashed components of the
HTTP request, the protected resource MUST re-create and verify a hash
for each component as described below. This process is a mirror of
the process used to create the hashes in the first place, with a mind
toward the fact that order may have changed and that elements may
have been added or deleted. The protected resource MUST similarly
compare the replicated values included in various JSON fields with
the corresponding actual values from the request. Failure to do so
will allow an attacker to modify the underlying request while at the
same time having the application layer verify the signature
correctly.
5.1. Validating the query parameter list and hash
The client has at its disposal a map that indexes the query parameter The client has at its disposal a map that indexes the query parameter
names to the values given. The client creates a string buffer for names to the values given. The client creates a string buffer for
calculating the hash. The client then iterates through the "list" calculating the hash. The client then iterates through the "list"
portion of the "p" parameter. For each item in the list (in the portion of the "p" parameter. For each item in the list (in the
order of the list) it does the following: order of the list) it does the following:
1. Fetch the value of the parameter from the HTTP request parameter 1. Fetch the value of the parameter from the HTTP request query
map. If a parameter is found in the list of signed parameters parameter map. If a parameter is found in the list of signed
but not in the map, the validation fails. parameters but not in the map, the validation fails.
2. Encode the parameter as "name=value" and concatenate it to the 2. Encode the parameter as "name=value" and concatenate it to the
end of the string buffer. [[same separator issue as above.]] end of the string buffer, separated by an ampersand character.
The client calculates the hash of the string buffer and base64url The client calculates the hash of the string buffer and base64url
encodes it. The client compares that string to the string passed in encodes it. The protected resource compares that string to the
as the hash. If the two match, the hash validates, and all named string passed in as the hash. If the two match, the hash validates,
parameters and their values are considered covered by the signature. and all named parameters and their values are considered covered by
the signature.
There MAY be additional query parameters that are not listed in the There MAY be additional query parameters that are not listed in the
list and are therefore not covered by the signature. The client MUST list and are therefore not covered by the signature. The client MUST
decide whether or not to accept a request with these uncovered decide whether or not to accept a request with these uncovered
parameters. parameters.
4.2. Validating the header list and hash 5.2. Validating the header list and hash
The client has at its disposal a map that indexes the header names to The client has at its disposal a map that indexes the header names to
the values given. The client creates a string buffer for calculating the values given. The client creates a string buffer for calculating
the hash. The client then iterates through the "list" portion of the the hash. The client then iterates through the "list" portion of the
"h" parameter. For each item in the list (in the order of the list) "h" parameter. For each item in the list (in the order of the list)
it does the following: it does the following:
1. Fetch the value of the header from the HTTP request header map. 1. Fetch the value of the header from the HTTP request header map.
If a header is found in the list of signed parameters but not in If a header is found in the list of signed parameters but not in
the map, the validation fails. the map, the validation fails.
2. Encode the parameter as "name: value" and concatenate it to the 2. Encode the parameter as "name: value" and concatenate it to the
end of the string buffer. [[same separator issue as above.]] end of the string buffer, separated by a newline character.
The client calculates the hash of the string buffer and base64url The client calculates the hash of the string buffer and base64url
encodes it. The client compares that string to the string passed in encodes it. The protected resource compares that string to the
as the hash. If the two match, the hash validates, and all named string passed in as the hash. If the two match, the hash validates,
headers and their values are considered covered by the signature. and all named headers and their values are considered covered by the
signature.
There MAY be additional headers that are not listed in the list and There MAY be additional headers that are not listed in the list and
are therefore not covered by the signature. The client MUST decide are therefore not covered by the signature. The client MUST decide
whether or not to accept a request with these uncovered headers. whether or not to accept a request with these uncovered headers.
5. Example
Example goes in here but will look like something like this
(symmetric key case).
1) HTTP Request (plain)
POST /request?b5=%3D%253D&a3=a&c%40=&a2=r%20b&c2 HTTP/1.1
Host: example.com
2) JWS protected JSON object
{"typ":"pop",
"alg":"HS256",
"kid":"client12345@example.com"}
.
{"m":"POST",
"u":"example.com",
"p":"request",
"q":[["a3", "b5", "a2"], "m2398f32i2o3roiu2313aa"],
"ts":1300819380
}
.
dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk
Figure 2: Message Flow.
6. IANA Considerations 6. IANA Considerations
6.1. The 'pop' OAuth Access Token Type 6.1. The 'pop' OAuth Access Token Type
Section 11.1 of [RFC6749] defines the OAuth Access Token Type Section 11.1 of [RFC6749] defines the OAuth Access Token Type
Registry and this document adds another token type to this registry. Registry and this document adds another token type to this registry.
Type name: pop Type name: pop
Additional Token Endpoint Response Parameters: (none) Additional Token Endpoint Response Parameters: (none)
skipping to change at page 8, line 6 skipping to change at page 9, line 4
Registry and this document adds another token type to this registry. Registry and this document adds another token type to this registry.
Type name: pop Type name: pop
Additional Token Endpoint Response Parameters: (none) Additional Token Endpoint Response Parameters: (none)
HTTP Authentication Scheme(s): Proof-of-possession access token for HTTP Authentication Scheme(s): Proof-of-possession access token for
use with OAuth 2.0 use with OAuth 2.0
Change controller: IETF Change controller: IETF
Specification document(s): [[ this document ]] Specification document(s): [[ this document ]]
6.2. JSON Web Signature and Encryption Type Values Registration 6.2. JSON Web Signature and Encryption Type Values Registration
This specification registers the "pop" type value in the IANA JSON This specification registers the "pop" type value in the IANA JSON
Web Signature and Encryption Type Values registry Web Signature and Encryption Type Values registry [RFC7515]:
[I-D.ietf-jose-json-web-signature]:
o "typ" Header Parameter Value: "pop" o "typ" Header Parameter Value: "pop"
o Abbreviation for MIME Type: None o Abbreviation for MIME Type: None
o Change Controller: IETF o Change Controller: IETF
o Specification Document(s): [[ this document ]] o Specification Document(s): [[ this document ]]
7. Security Considerations 7. Security Considerations
skipping to change at page 8, line 38 skipping to change at page 9, line 34
This specification can be used with and without Transport Layer This specification can be used with and without Transport Layer
Security (TLS). Security (TLS).
Without TLS this protocol provides a mechanism for verifying the Without TLS this protocol provides a mechanism for verifying the
integrity of requests, it provides no confidentiality protection. integrity of requests, it provides no confidentiality protection.
Consequently, eavesdroppers will have full access to communication Consequently, eavesdroppers will have full access to communication
content and any further messages exchanged between the client and the content and any further messages exchanged between the client and the
resource server. This could be problematic when data is exchanged resource server. This could be problematic when data is exchanged
that requires care, such as personal data. that requires care, such as personal data.
When TLS is used then confidentiality can be ensured; this version of When TLS is used then confidentiality of the transmission can be
the specification does, however, not provide the TLS channel binding ensured between endpoints, including both the request and the
feature, which ensures that the TLS channel is cryptographically response. The use of TLS in combination with the signed HTTP request
bound to the application layer protocol authentication defined in mechanism is highly recommended to ensure the confidentiality of the
this document. data returned from the protected resource.
The use of TLS in combination with the signed HTTP request mechanism
is highly recommended to ensure the confidentiality of the user's
data.
7.2. Authentication of Resource Servers
This protocol allows clients to verify the authenticity of resource
servers only when TLS is used. With TLS the resource server is
authenticated as part of the TLS handshake. The mechanism described
in this document does not provide any mechanism for the client to
authenticate the resource server at the application layer.
7.3. Plaintext Storage of Credentials
The mechanism described in this document works similar to many three 7.2. Plaintext Storage of Credentials
party authentication and key exchange mechanisms. In order to
compute the signature over the HTTP request, the client must have
access to a key bound to the access token (in plaintext form).
If an attacker were to gain access to these stored secrets at the The mechanism described in this document works in a similar way to
client or (in case of symmetric keys) at the resource server he or many three-party authentication and key exchange mechanisms. In
she would be able to perform any action on behalf of any client. order to compute the signature over the HTTP request, the client must
have access to a key bound to the access token in plaintext form. If
an attacker were to gain access to these stored secrets at the client
or (in case of symmetric keys) at the resource server they would be
able to perform any action on behalf of any client just as if they
had stolen a bearer token.
It is therefore paramount to the security of the protocol that the It is therefore paramount to the security of the protocol that the
private keys associated with the access tokens are protected from private keys associated with the access tokens are protected from
unauthorized access. unauthorized access.
7.4. Entropy of Keys 7.3. Entropy of Keys
Unless TLS is used between the client and the resource server, Unless TLS is used between the client and the resource server,
eavesdroppers will have full access to requests sent by the client. eavesdroppers will have full access to requests sent by the client.
They will thus be able to mount off-line brute-force attacks to They will thus be able to mount off-line brute-force attacks to
recover the session key or private key used to compute the keyed attempt recovery of the session key or private key used to compute
message digest or digital signature, respectively. the keyed message digest or digital signature, respectively.
This specification assumes that the keying material for use with the This specification assumes that the key used herein has been
described HTTP signing mechanism has been distributed via other distributed via other mechanisms, such as
mechanisms, such as [I-D.bradley-oauth-pop-key-distribution]. Hence, [I-D.ietf-oauth-pop-key-distribution]. Hence, it is the
it is the responsibility of the authorization server and or the responsibility of the authorization server and or the client to be
client to be careful when generating fresh and unique keys with careful when generating fresh and unique keys with sufficient entropy
sufficient entropy to resist such attacks for at least the length of to resist such attacks for at least the length of time that the
time that the session keys (and the access tokens) are valid. session keys (and the access tokens) are valid.
For example, if the key bound to the access token is valid for one For example, if the key bound to the access token is valid for one
day, authorization servers must ensure that it is not possible to day, authorization servers must ensure that it is not possible to
mount a brute force attack that recovers that key in less than one mount a brute force attack that recovers that key in less than one
day. Of course, servers are urged to err on the side of caution, and day. Of course, servers are urged to err on the side of caution, and
use the longest key length reasonable. use the longest key length possible within reason.
7.5. Denial of Service 7.4. Denial of Service
This specification includes a number of features which may make This specification includes a number of features which may make
resource exhaustion attacks against resource servers possible. For resource exhaustion attacks against resource servers possible. For
example, a resource server may need to need to the resource server example, a resource server may need to process the incoming request,
has to process the incoming request, verify the access token, perform verify the access token, perform signature verification, and might
signature verification, and might have (in certain circumstances) (in certain circumstances) have to consult back-end databases or the
consult back-end databases or the authorization server before authorization server before granting access to the protected
granting access to the protected resource. resource. Many of these actions are shared with bearer tokens, but
the additional cryptographic overhead of validating the signed
request needs to be taken into consideration with deployment of this
specification.
An attacker may exploit this to perform a denial of service attack by An attacker may exploit this to perform a denial of service attack by
sending a large number of invalid requests to the server. The sending a large number of invalid requests to the server. The
computational overhead of verifying the keyed message digest alone computational overhead of verifying the keyed message digest alone is
is, however, not sufficient to mount a denial of service attack since not likely sufficient to mount a denial of service attack. To help
keyed message digest functions belong to the computationally fastest combat this, it is RECOMMENDED that the protected resource validate
cryptographic algorithms. The situation may, however, be different the access token (contained in the "at" member of the signed
when using asymmetric cryptography, which is also supported by the structure) before performing any cryptographic verification
JWS. calculations.
7.6. Protecting HTTP Header Fields 7.5. Validating the integrity of HTTP Headers and Query Parameters
This specification provides flexibility for selectively protecting This specification provides flexibility for selectively validating
header fields and even the body of the message. Since all components the integrity of header fields and message bodies. Since all
of the HTTP request are only optionally protected by this method, and components of the HTTP request are only optionally validated by this
even some components may be protected only in part (e.g., some method, and even some components may be validated only in part (e.g.,
headers but not others) it is up to application developers to verify some headers but not others) it is up to protected resource
that any parameters in a request are actually covered by the developers to verify that any vital parameters in a request are
signature. actually covered by the signature.
The application verifying this signature MUST NOT assume that any The application verifying this signature MUST NOT assume that any
particular parameter is appropriately covered by the signature. Any particular parameter is appropriately covered by the signature unless
it is included in the signed structure and the hash is verified. Any
applications that are sensitive of header or query parameter order applications that are sensitive of header or query parameter order
MUST verify the order of the parameters on their own. The MUST verify the order of the parameters on their own. The
application MUST also compare the values in the JSON container with application MUST also compare the values in the JSON container with
the actual parameters received with the HTTP request. Failure to the actual parameters received with the HTTP request (using a direct
make this comparison will render the signature mechanism useless. comparison or a hash calculation, as appropriate). Failure to make
this comparison will render the signature mechanism useless for
protecting these elements.
8. Acknowledgements The behavior of repeated query parameters or repeated HTTP headers is
undefined by this specification. If a header or query parameter is
repeated on either the outgoing request from the client or the
incoming request to the protected resource, that query parameter or
header name MUST NOT be covered by the hash and signature. [[ Note to
the WG: is this something we need to cover? ]]
The authors acknowledge the OAuth Working Group and submit this draft This specification records the order in which query parameters and
for feedback and input into the ongoing work of signed HTTP requests headers are hashed, but it does not guarantee that order is preserved
for the interaction between clients and resource servers. between the client and protected resource.
9. References 8. Privacy Considerations
9.1. Normative References This specification addresses machine to machine communications and
raises no privacy considerations beyond existing OAuth transactions.
[I-D.ietf-jose-json-web-signature] 9. Acknowledgements
Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", draft-ietf-jose-json-web-signature-41 The authors thank the OAuth Working Group for input into this work.
(work in progress), January 2015.
10. Normative References
[I-D.ietf-oauth-pop-architecture]
Hunt, P., Richer, J., Mills, W., Mishra, P., and H.
Tschofenig, "OAuth 2.0 Proof-of-Possession (PoP) Security
Architecture", draft-ietf-oauth-pop-architecture-07 (work
in progress), December 2015.
[I-D.ietf-oauth-pop-key-distribution]
Bradley, J., Hunt, P., Jones, M., and H. Tschofenig,
"OAuth 2.0 Proof-of-Possession: Authorization Server to
Client Key Distribution", draft-ietf-oauth-pop-key-
distribution-02 (work in progress), October 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
6749, October 2012. RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization [RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750, October 2012. Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012,
<http://www.rfc-editor.org/info/rfc6750>.
9.2. Informative References [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>.
[I-D.bradley-oauth-pop-key-distribution] [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Bradley, J., Hunt, P., Jones, M., and H. Tschofenig, Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
"OAuth 2.0 Proof-of-Possession: Authorization Server to 2015, <http://www.rfc-editor.org/info/rfc7515>.
Client Key Distribution", draft-bradley-oauth-pop-key-
distribution-01 (work in progress), June 2014.
[I-D.hunt-oauth-pop-architecture] [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
Hunt, P., Richer, J., Mills, W., Mishra, P., and H. (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
Tschofenig, "OAuth 2.0 Proof-of-Possession (PoP) Security <http://www.rfc-editor.org/info/rfc7519>.
Architecture", draft-hunt-oauth-pop-architecture-02 (work
in progress), June 2014. [RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection",
RFC 7662, DOI 10.17487/RFC7662, October 2015,
<http://www.rfc-editor.org/info/rfc7662>.
Authors' Addresses Authors' Addresses
Justin Richer (editor) Justin Richer (editor)
Email: ietf@justin.richer.org Email: ietf@justin.richer.org
John Bradley John Bradley
Ping Identity Ping Identity
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