< draft-myers-auth-sasl-12.txt		draft-myers-auth-sasl-13.txt >
			This Internet-Draft was published as a Proposed Standard RFC, RFC 2222
			(http://www.ietf.org/rfc/rfc2222.txt), on 1997-10-29.
	Network Working Group J. Myers		The name of the internet-draft was draft-myers-auth-sasl-12.txt
	Internet Draft September 1997
	Document: draft-myers-auth-sasl-12.txt
	Simple Authentication and Security Layer (SASL)
	Status of this Memo
	This document is an Internet Draft. Internet Drafts are working
	documents of the Internet Engineering Task Force (IETF), its Areas,
	and its Working Groups. Note that other groups may also distribute
	working documents as Internet Drafts.
	Internet Drafts are draft documents valid for a maximum of six
	months. Internet Drafts may be updated, replaced, or obsoleted by
	other documents at any time. It is not appropriate to use Internet
	Drafts as reference material or to cite them other than as a
	``working draft'' or ``work in progress``.
	To learn the current status of any Internet-Draft, please check the
	1id-abstracts.txt listing contained in the Internet-Drafts Shadow
	Directories on ds.internic.net, nic.nordu.net, ftp.isi.edu, or
	munnari.oz.au.
	A revised version of this draft document will be submitted to the RFC
	editor as a Proposed Standard for the Internet Community. Discussion
	and suggestions for improvement are requested. This document will
	expire before December 1996. Distribution of this draft is
	unlimited.
	Internet DRAFT SASL September 9, 1997
	1. Abstract
	This document describes a method for adding authentication support to
	connection-based protocols. To use this specification, a protocol
	includes a command for identifying and authenticating a user to a
	server and for optionally negotiating protection of subsequent
	protocol interactions. If its use is negotiated, a security layer is
	inserted between the protocol and the connection. This document
	describes how a protocol specifies such a command, defines several
	mechanisms for use by the command, and defines the protocol used for
	carrying a negotiated security layer over the connection.
	2. Organization of this Document
	2.1. How to Read This Document
	This document is written to serve two different audiences, protocol
	designers using this specification to support authentication in their
	protocol, and implementors of clients or servers for those protocols
	using this specification.
	The sections "Introduction and Overview", "Profiling requirements",
	and "Security Considerations" cover issues that protocol designers
	need to understand and address in profiling this specification for
	use in a specific protocol.
	Implementors of a protocol using this specification need the
	protocol-specific profiling information in addition to the
	information in this document.
	2.2. Conventions Used in this Document
	In examples, "C:" and "S:" indicate lines sent by the client and
	server respectively.
	The following terms are used in this document to signify the
	requirements of this specification.
	1) MUST, or the adjective REQUIRED, means that the definition is an
	absolute requirement of the specification.
	2) MUST NOT that the definition is an absolute prohibition of the
	specification.
	3) SHOULD means that there may exist valid reasons in particular
	circumstances to ignore a particular item, but the full implications
	MUST be understood and carefully weighed before choosing a different
	course.
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	4) SHOULD NOT means that there may exist valid reasons in particular
	circumstances when the particular behavior is acceptable or even
	useful, but the full implications SHOULD be understood and the case
	carefully weighed before implementing any behavior described with
	this label.
	5) MAY, or the adjective OPTIONAL, means that an item is truly
	optional. One vendor may choose to include the item because a
	particular marketplace requires it or because the vendor feels that
	it enhances the product while another vendor may omit the same item.
	An implementation which does not include a particular option MUST be
	prepared to interoperate with another implementation which does
	include the option.
	"Can" is used instead of "may" when referring to a possible
	circumstance or situation, as opposed to an optional facility of the
	protocol.
	2.3. Examples
	Examples in this document are for the IMAP profile [IMAP4] of this
	specification. The base64 encoding of challenges and responses, as
	well as the "+ " preceding the responses are part of the IMAP4
	profile, not part of the SASL specification itself.
	3. Introduction and Overview
	The Simple Authentication and Security Layer (SASL) is a method for
	adding authentication support to connection-based protocols. To use
	this specification, a protocol includes a command for identifying and
	authenticating a user to a server and for optionally negotiating a
	security layer for subsequent protocol interactions.
	The command has a required argument identifying a SASL mechanism.
	SASL mechanisms are named by strings, from 1 to 20 characters in
	length, consisting of upper-case letters, digits, hyphens, and/or
	underscores. SASL mechanism names must be registered with the IANA.
	Procedures for registering new SASL mechanisms are given in the
	section "Registration procedures"
	If a server supports the requested mechanism, it initiates an
	authentication protocol exchange. This consists of a series of
	server challenges and client responses that are specific to the
	requested mechanism. The challenges and responses are defined by the
	mechanisms as binary tokens of arbitrary length. The protocol's
	profile then specifies how these binary tokens are then encoded for
	transfer over the connection.
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	After receiving the authentication command or any client response, a
	server may issue a challenge, indicate failure, or indicate
	completion. The protocol's profile specifies how the server
	indicates which of the above it is doing.
	After receiving a challenge, a client may issue a response or abort
	the exchange. The protocol's profile specifies how the client
	indicates which of the above it is doing.
	During the authentication protocol exchange, the mechanism performs
	authentication, transmits an authorization identity (frequently known
	as a userid) from the client to server, and negotiates the use of a
	mechanism-specific security layer. If the use of a security layer is
	agreed upon, then the mechanism must also define or negotiate the
	maximum cipher-text buffer size that each side is able to receive.
	The transmitted authorization identity may be different than the
	identity in the client's authentication credentials. This permits
	agents such as proxy servers to authenticate using their own
	credentials, yet request the access privileges of the identity for
	which they are proxying. With any mechanism, transmitting an
	authorization identity of the empty string directs the server to
	derive an authorization identity from the client's authentication
	credentials.
	If use of a security layer is negotiated, it is applied to all
	subsequent data sent over the connection. The security layer takes
	effect immediately following the last response of the authentication
	exchange for data sent by the client and the completion indication
	for data sent by the server. Once the security layer is in effect,
	the protocol stream is processed by the security layer into buffers
	of cipher-text. Each buffer is transferred over the connection as a
	stream of octets prepended with a four octet field in network byte
	order that represents the length of the following buffer. The length
	of the cipher-text buffer must be no larger than the maximum size
	that was defined or negotiated by the other side.
	4. Profiling requirements
	In order to use this specification, a protocol definition must supply
	the following information:
	1. A service name, to be selected from the IANA registry of "service"
	elements for the GSSAPI host-based service name form. [GSSAPI]
	2. A definition of the command to initiate the authentication
	protocol exchange. This command must have as a parameter the
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	mechanism name being selected by the client.
	The command SHOULD have an optional parameter giving an initial
	response. This optional parameter allows the client to avoid a
	round trip when using a mechanism which is defined to have the
	client send data first. When this initial response is sent by the
	client and the selected mechanism is defined to have the server
	start with an initial challenge, the command fails. See section
	5.1 of this document for further information.
	3. A definition of the method by which the authentication protocol
	exchange is carried out, including how the challenges and
	responses are encoded, how the server indicates completion or
	failure of the exchange, how the client aborts an exchange, and
	how the exchange method interacts with any line length limits in
	the protocol.
	4. Identification of the octet where any negotiated security layer
	starts to take effect, in both directions.
	5. A specification of how the authorization identity passed from the
	client to the server is to be interpreted.
	5. Specific issues
	5.1. Client sends data first
	Some mechanisms specify that the first data sent in the
	authentication protocol exchange is from the client to the server.
	If a protocol's profile permits the command which initiates an
	authentication protocol exchange to contain an initial client
	response, this parameter SHOULD be used with such mechanisms.
	If the initial client response parameter is not given, or if a
	protocol's profile does not permit the command which initiates an
	authentication protocol exchange to contain an initial client
	response, then the server issues a challenge with no data. The
	client's response to this challenge is then used as the initial
	client response. (The server then proceeds to send the next
	challenge, indicates completion, or indicates failure.)
	5.2. Server returns success with additional data
	Some mechanisms may specify that server challenge data be sent to the
	client along with an indication of successful completion of the
	exchange. This data would, for example, authenticate the server to
	the client.
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	If a protocol's profile does not permit this server challenge to be
	returned with a success indication, then the server issues the server
	challenge without an indication of successful completion. The client
	then responds with no data. After receiving this empty response, the
	server then indicates successful completion.
	5.3. Multiple authentications
	Unless otherwise stated by the protocol's profile, only one
	successful SASL negotiation may occur in a protocol session. In this
	case, once an authentication protocol exchange has successfully
	completed, further attempts to initiate an authentication protocol
	exchange fail.
	In the case that a profile explicitly permits multiple successful
	SASL negotiations to occur, then in no case may multiple security
	layers be simultaneously in effect. If a security layer is in effect
	and a subsequent SASL negotiation selects no security layer, the
	original security layer remains in effect. If a security layer is in
	effect and a subsequent SASL negotiation selects a second security
	layer, then the second security layer replaces the first.
	6. Registration procedures
	Registration of a SASL mechanism is done by filling in the template
	in section 6.4 and sending it in to iana@isi.edu. IANA has the right
	to reject obviously bogus registrations, but will perform no review
	of clams made in the registration form.
	There is no naming convention for SASL mechanisms; any name that
	conforms to the syntax of a SASL mechanism name can be registered.
	While the registration procedures do not require it, authors of SASL
	mechanisms are encouraged to seek community review and comment
	whenever that is feasible. Authors may seek community review by
	posting a specification of their proposed mechanism as an internet-
	draft. SASL mechanisms intended for widespread use should be
	standardized through the normal IETF process, when appropriate.
	6.1. Comments on SASL mechanism registrations
	Comments on registered SASL mechanisms should first be sent to the
	"owner" of the mechanism. Submitters of comments may, after a
	reasonable attempt to contact the owner, request IANA to attach their
	comment to the SASL mechanism registration itself. If IANA approves
	of this the comment will be made accessible in conjunction with the
	SASL mechanism registration itself.
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	6.2. Location of Registered SASL Mechanism List
	SASL mechanism registrations will be posted in the anonymous FTP
	directory
	"ftp://ftp.isi.edu/in-notes/iana/assignments/sasl-mechanisms/" and
	all registered SASL mechanisms will be listed in the periodically
	issued "Assigned Numbers" RFC [currently RFC-1700]. The SASL
	mechanism description and other supporting material may also be
	published as an Informational RFC by sending it to
	"rfc-editor@isi.edu" (please follow the instructions to RFC authors
	[RFC-1543]).
	6.3. Change Control
	Once a SASL mechanism registration has been published by IANA, the
	author may request a change to its definition. The change request
	follows the same procedure as the registration request.
	The owner of a SASL mechanism may pass responsibility for the SASL
	mechanism to another person or agency by informing IANA; this can be
	done without discussion or review.
	The IESG may reassign responsibility for a SASL mechanism. The most
	common case of this will be to enable changes to be made to
	mechanisms where the author of the registration has died, moved out
	of contact or is otherwise unable to make changes that are important
	to the community.
	SASL mechanism registrations may not be deleted; mechanisms which are
	no longer believed appropriate for use can be declared OBSOLETE by a
	change to their "intended use" field; such SASL mechanisms will be
	clearly marked in the lists published by IANA.
	The IESG is considered to be the owner of all SASL mechanisms which
	are on the IETF standards track.
	6.4. Registration Template
	To: iana@isi.edu
	Subject: Registration of SASL mechanism X
	SASL mechanism name:
	Security considerations:
	Published specification (optional, recommended):
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	Person & email address to contact for further information:
	Intended usage:
	(One of COMMON, LIMITED USE or OBSOLETE)
	Author/Change controller:
	(Any other information that the author deems interesting may be
	added below this line.)
	7. Mechanism definitions
	The following mechanisms are hereby defined.
	7.1. Kerberos version 4 mechanism
	The mechanism name associated with Kerberos version 4 is
	"KERBEROS_V4".
	The first challenge consists of a random 32-bit number in network
	byte order. The client responds with a Kerberos ticket and an
	authenticator for the principal "service.hostname@realm", where
	"service" is the service name specified in the protocol's profile,
	"hostname" is the first component of the host name of the server with
	all letters in lower case, and where "realm" is the Kerberos realm of
	the server. The encrypted checksum field included within the
	Kerberos authenticator contains the server provided challenge in
	network byte order.
	Upon decrypting and verifying the ticket and authenticator, the
	server verifies that the contained checksum field equals the original
	server provided random 32-bit number. Should the verification be
	successful, the server must add one to the checksum and construct 8
	octets of data, with the first four octets containing the incremented
	checksum in network byte order, the fifth octet containing a bit-mask
	specifying the security layers supported by the server, and the sixth
	through eighth octets containing, in network byte order, the maximum
	cipher-text buffer size the server is able to receive. The server
	must encrypt using DES ECB mode the 8 octets of data in the session
	key and issue that encrypted data in a second challenge. The client
	considers the server authenticated if the first four octets of the
	un-encrypted data is equal to one plus the checksum it previously
	sent.
	The client must construct data with the first four octets containing
	the original server-issued checksum in network byte order, the fifth
	octet containing the bit-mask specifying the selected security layer,
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	the sixth through eighth octets containing in network byte order the
	maximum cipher-text buffer size the client is able to receive, and
	the following octets containing the authorization identity. The
	client must then append from one to eight zero-valued octets so that
	the length of the data is a multiple of eight octets. The client must
	then encrypt using DES PCBC mode the data with the session key and
	respond with the encrypted data. The server decrypts the data and
	verifies the contained checksum. The server must verify that the
	principal identified in the Kerberos ticket is authorized to connect
	as that authorization identity. After this verification, the
	authentication process is complete.
	The security layers and their corresponding bit-masks are as follows:
	1 No security layer
	2 Integrity (krb_mk_safe) protection
	4 Privacy (krb_mk_priv) protection
	Other bit-masks may be defined in the future; bits which are not
	understood must be negotiated off.
	EXAMPLE: The following are two Kerberos version 4 login scenarios to
	the IMAP4 protocol (note that the line breaks in the sample
	authenticators are for editorial clarity and are not in real
	authenticators)
	S: * OK IMAP4 Server
	C: A001 AUTHENTICATE KERBEROS_V4
	S: + AmFYig==
	C: BAcAQU5EUkVXLkNNVS5FRFUAOCAsho84kLN3/IJmrMG+25a4DT
	+nZImJjnTNHJUtxAA+o0KPKfHEcAFs9a3CL5Oebe/ydHJUwYFd
	WwuQ1MWiy6IesKvjL5rL9WjXUb9MwT9bpObYLGOKi1Qh
	S: + or//EoAADZI=
	C: DiAF5A4gA+oOIALuBkAAmw==
	S: A001 OK Kerberos V4 authentication successful
	S: * OK IMAP4 Server
	C: A001 AUTHENTICATE KERBEROS_V4
	S: + gcfgCA==
	C: BAcAQU5EUkVXLkNNVS5FRFUAOCAsho84kLN3/IJmrMG+25a4DT
	+nZImJjnTNHJUtxAA+o0KPKfHEcAFs9a3CL5Oebe/ydHJUwYFd
	WwuQ1MWiy6IesKvjL5rL9WjXUb9MwT9bpObYLGOKi1Qh
	S: A001 NO Kerberos V4 authentication failed
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	7.2. GSSAPI mechanism
	The mechanism name associated with all mechanisms employing the
	GSSAPI [GSSAPI] is "GSSAPI".
	7.2.1 Client side of authentication protocol exchange
	The client calls GSS_Init_sec_context, passing in 0 for
	input_context_handle (initially) and a targ_name equal to output_name
	from GSS_Import_Name called with input_name_type of
	GSS_C_NT_HOSTBASED_SERVICE and input_name_string of
	"service@hostname" where "service" is the service name specified in
	the protocol's profile, and "hostname" is the fully qualified host
	name of the server. The client then responds with the resulting
	output_token. If GSS_Init_sec_context returns GSS_S_CONTINUE_NEEDED,
	then the client should expect the server to issue a token in a
	subsequent challenge. The client must pass the token to another call
	to GSS_Init_sec_context, repeating the actions in this paragraph.
	When GSS_Init_sec_context returns GSS_S_COMPLETE, the client takes
	the following actions: If the last call to GSS_Init_sec_context
	returned an output_token, then the client responds with the
	output_token, otherwise the client responds with no data. The client
	should then expect the server to issue a token in a subsequent
	challenge. The client passes this token to GSS_Unwrap and interprets
	the first octet of resulting cleartext as a bit-mask specifying the
	security layers supported by the server and the second through fourth
	octets as the maximum size output_message to send to the server. The
	client then constructs data, with the first octet containing the
	bit-mask specifying the selected security layer, the second through
	fourth octets containing in network byte order the maximum size
	output_message the client is able to receive, and the remaining
	octets containing the authorization identity. The client passes the
	data to GSS_Wrap with conf_flag set to FALSE, and responds with the
	generated output_message. The client can then consider the server
	authenticated.
	7.2.2 Server side of authentication protocol exchange
	The server passes the initial client response to
	GSS_Accept_sec_context as input_token, setting input_context_handle
	to 0 (initially). If GSS_Accept_sec_context returns
	GSS_S_CONTINUE_NEEDED, the server returns the generated output_token
	to the client in challenge and passes the resulting response to
	another call to GSS_Accept_sec_context, repeating the actions in this
	paragraph.
	When GSS_Accept_sec_context returns GSS_S_COMPLETE, the client takes
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	the following actions: If the last call to GSS_Accept_sec_context
	returned an output_token, the server returns it to the client in a
	challenge and expects a reply from the client with no data. Whether
	or not an output_token was returned (and after receipt of any
	response from the client to such an output_token), the server then
	constructs 4 octets of data, with the first octet containing a bit-
	mask specifying the security layers supported by the server and the
	second through fourth octets containing in network byte order the
	maximum size output_token the server is able to receive. The server
	must then pass the plaintext to GSS_Wrap with conf_flag set to FALSE
	and issue the generated output_message to the client in a challenge.
	The server must then pass the resulting response to GSS_Unwrap and
	interpret the first octet of resulting cleartext as the bit-mask for
	the selected security layer, the second through fourth octets as the
	maximum size output_message to send to the client, and the remaining
	octets as the authorization identity. The server must verify that
	the src_name is authorized to authenticate as the authorization
	identity. After these verifications, the authentication process is
	complete.
	7.2.3 Security layer
	The security layers and their corresponding bit-masks are as follows:
	1 No security layer
	2 Integrity protection.
	Sender calls GSS_Wrap with conf_flag set to FALSE
	4 Privacy protection.
	Sender calls GSS_Wrap with conf_flag set to TRUE
	Other bit-masks may be defined in the future; bits which are not
	understood must be negotiated off.
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	7.3. S/Key mechanism
	The mechanism name associated with S/Key [SKEY] using the MD4 digest
	algorithm is "SKEY".
	The client sends an initial response with the authorization identity.
	The server then issues a challenge which contains the decimal
	sequence number followed by a single space and the seed string for
	the indicated authorization identity. The client responds with the
	one-time-password, as either a 64-bit value in network byte order or
	encoded in the "six English words" format.
	The server must verify the one-time-password. After this
	verification, the authentication process is complete.
	S/Key authentication does not provide for any security layers.
	EXAMPLE: The following are two S/Key login scenarios in the IMAP4
	protocol.
	S: * OK IMAP4 Server
	C: A001 AUTHENTICATE SKEY
	S: +
	C: bW9yZ2Fu
	S: + OTUgUWE1ODMwOA==
	C: Rk9VUiBNQU5OIFNPT04gRklSIFZBUlkgTUFTSA==
	S: A001 OK S/Key authentication successful
	S: * OK IMAP4 Server
	C: A001 AUTHENTICATE SKEY
	S: +
	C: c21pdGg=
	S: + OTUgUWE1ODMwOA==
	C: BsAY3g4gBNo=
	S: A001 NO S/Key authentication failed
	The following is an S/Key login scenario in an IMAP4-like protocol
	which has an optional "initial response" argument to the AUTHENTICATE
	command.
	S: * OK IMAP4-Like Server
	C: A001 AUTHENTICATE SKEY bW9yZ2Fu
	S: + OTUgUWE1ODMwOA==
	C: Rk9VUiBNQU5OIFNPT04gRklSIFZBUlkgTUFTSA==
	S: A001 OK S/Key authentication successful
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	7.4. External mechanism
	The mechanism name associated with external authentication is
	"EXTERNAL".
	The client sends an initial response with the authorization identity.
	The server uses information, external to SASL, to determine whether
	the client is authorized to authenticate as the authorization
	identity. If the client is so authorized, the server indicates
	successful completion of the authentication exchange; otherwise the
	server indicates failure.
	The system providing this external information may be, for example,
	IPsec or TLS.
	If the client sends the empty string as the authorization identity
	(thus requesting the authorization identity be derived from the
	client's authentication credentials), the authorization identity is
	to be derived from authentication credentials which exist in the
	system which is providing the external authentication.
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	8. References
	[IMAP4] Crispin, M., "Internet Message Access Protocol - Version 4",
	RFC 1730, University of Washington, December 1994.
	[GSSAPI] Linn, J., "Generic Security Service Application Program
	Interface, Version 2", RFC 2078, January 1997
	[RFC-1543] Postel, J., "Instructions to RFC Authors", RFC 1543,
	October 1993
	[SKEY] Haller, Neil M. "The S/Key One-Time Password System", RFC
	1760, Bellcore, February 1995
	9. Security Considerations
	Security issues are discussed throughout this memo.
	The mechanisms that support integrity protection are designed such
	that the negotiation of the security layer and authorization identity
	is integrity protected. When the client selects a security layer
	with at least integrity protection, this protects against an active
	attacker hijacking the connection and modifying the authentication
	exchange to negotiate a plaintext connection.
	When a server or client supports multiple authentication mechanisms,
	each of which has a different security strength, it is possible for
	an active attacker to cause a party to use the least secure mechanism
	supported. To protect against this sort of attack, a client or
	server which supports mechanisms of different strengths should have a
	configurable minimum strength that it will use. It is not sufficient
	for this minimum strength check to only be on the server, since an
	active attacker can change which mechanisms the client sees as being
	supported, causing the client to send authentication credentials for
	its weakest supported mechanism.
	The client's selection of a SASL mechanism is done in the clear and
	may be modified by an active attacker. It is important for any new
	SASL mechanisms to be designed such that an active attacker cannot
	obtain an authentication with weaker security properties by modifying
	the SASL mechanism name and/or the challenges and responses.
	Any protocol interactions prior to authentication are performed in
	the clear and may be modified by an active attacker. In the case
	where a client selects integrity protection, it is important that any
	security-sensitive protocol negotiations be performed after
	authentication is complete. Protocols should be designed such that
	negotiations performed prior to authentication should be either
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	ignored or revalidated once authentication is complete.
	10. Author's Address
	John G. Myers
	Netscape Communications
	501 E. Middlefield Road
	Mail Stop MV-029
	Mountain View, CA 94043-4042
	Email: jgmyers@netscape.com
	Appendix A. Relation of SASL to Transport Security
	Questions have been raised about the relationship between SASL and
	various services (such as IPsec and TLS) which provide a secured
	connection.
	Two of the key features of SASL are:
	1. The separation of the authorization identity from the identity in
	the client's credentials. This permits agents such as proxy
	servers to authenticate using their own credentials, yet request
	the access privileges of the identity for which they are proxying.
	2. Upon successful completion of an authentication exchange, the
	server knows the authorization identity the client wishes to use.
	This allows servers to move to a "user is authenticated" state in
	the protocol.
	These features are extremely important to some application protocols,
	yet Transport Security services do not always provide them. To
	define SASL mechanisms based on these services would be a very messy
	task, as the framing of these services would be redundant with the
	framing of SASL and some method of providing these important SASL
	features would have to be devised.
	Sometimes it is desired to enable within an existing connection the
	use of a security service which does not fit the SASL model. (TLS is
	an example of such a service.) This can be done by adding a command,
	for example "STARTTLS", to the protocol. Such a command is outside
	the scope of SASL, and should be different from the command which
	starts a SASL authentication protocol exchange.
	In certain situations, it is reasonable to use SASL underneath one of
	these Transport Security services. The transport service would
	secure the connection, either service would authenticate the client,
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	and SASL would negotiate the authorization identity. The SASL
	negotiation would be what moves the protocol from "unauthenticated"
	to "authenticated" state. The "EXTERNAL" SASL mechanism is
	explicitly intended to handle the case where the transport service
	secures the connection and authenticates the client and SASL
	negotiates the authorization identity.
	When using SASL underneath a sufficiently strong Transport Security
	service, a SASL security layer would most likely be redundant. The
	client and server would thus probably want to negotiate off the use
	of a SASL security layer.
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	Table of Contents
	Status of this Memo ............................................... i
	1. Abstract .................................................... 2
	2. Organization of this Document ............................... 2
	2.1. How to Read This Document ................................... 2
	2.2. Conventions Used in this Document ........................... 2
	2.3. Examples .................................................... 3
	3. Introduction and Overview ................................... 3
	4. Profiling requirements ...................................... 4
	5. Specific issues ............................................. 5
	5.1. Client sends data first ..................................... 5
	5.2. Server returns success with additional data ................. 5
	5.3. Multiple authentications .................................... 6
	6. Registration procedures ..................................... 6
	6.1. Comments on SASL mechanism registrations .................... 6
	6.2. Location of Registered SASL Mechanism List .................. 7
	6.3. Change Control .............................................. 7
	6.4. Registration Template ....................................... 7
	7. Mechanism definitions ....................................... 8
	7.1. Kerberos version 4 mechanism ................................ 8
	7.2. GSSAPI mechanism ............................................ 10
	7.2.1 Client side of authentication protocol exchange ............. 10
	7.2.2 Server side of authentication protocol exchange ............. 10
	7.2.3 Security layer .............................................. 11
	7.3. S/Key mechanism ............................................. 12
	7.4. External mechanism .......................................... 13
	8. References .................................................. 14
	9. Security Considerations ..................................... 14
	10. Author's Address ............................................ 15
	Appendix A. Relation of SASL to Transport Security ................ 15
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