PCP D. Wing Internet-Draft T. Reddy Intended status: Standards Track P. Patil Expires: October 4, 2014 R. Penno Cisco April 2, 2014 PCP Extension for Third Party Authorization draft-wing-pcp-third-party-authz-03 Abstract It is often desirable for an application server to permit a flow across a firewall, as happens today when a firewall includes an Application Layer Gateway (ALG) function. However, an ALG has several weaknesses. This document describes a cryptographic technique for an application server to permit a flow across a firewall. This technique uses OAuth and a new PCP option. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on October 4, 2014. Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Wing, et al. Expires October 4, 2014 [Page 1] Internet-Draft PCP for 3rd party Authorization April 2014 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5 5. Obtaining a Token Using OAuth . . . . . . . . . . . . . . . . 6 5.1. ACCESS_TOKEN Option . . . . . . . . . . . . . . . . . . . 7 5.2. Generating the ACCESS_TOKEN option . . . . . . . . . . . 9 5.3. PCP server processing ACCESS_TOKEN option . . . . . . . . 10 5.4. Processing the PCP response . . . . . . . . . . . . . . . 11 6. PCP Server and Proxy behavior . . . . . . . . . . . . . . . . 11 7. Usage with PCP Authentication mechanism . . . . . . . . . . . 12 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . 13 11.2. Informative References . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 1. Introduction It is desirable for a third party to permit flows across a firewall. A typical use-case is a SIP proxy (which is aware of legitimate calls) which is not co-located with a firewall. Today, this functionality is provided by a firewall implementing a SIP-aware Application Layer Gateway function, which examines the SIP signaling to that SIP proxy and opens the appropriate pinholes for the RTP media. This has disadvantages, as described in detail in section Section 3. This document addresses requirement "Third Party Authorization" explained in section 4 of [I-D.reddy-pcp-auth-req]. This document proposes that a PCP [RFC6887] client communicate with an OAuth Authorization Server to obtain a cryptographic token for its media flow. That token is included in the PCP request and validated by the PCP server. Note: There is no relationship with the THIRD_PARTY option defined in [RFC6887], which serves a different purpose. THIRD_PARTY Option for Wing, et al. Expires October 4, 2014 [Page 2] Internet-Draft PCP for 3rd party Authorization April 2014 MAP and PEER Opcodes described in [RFC6887] is only applicable when all entities i.e the PCP client, PCP server and Application Server, are deployed within the same administrative domain. Since PCP server does not listen on a public interface, an Application Server outside the site will not be able to use THIRD_PARTY option to request services on behalf of the client. 2. Notational Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. WebRTC Server: A web server that supports WebRTC [I-D.ietf-rtcweb-overview]. 3. Problem Statement To protect networks using real-time communications, firewalls or session border controllers [RFC5853] are typically deployed. Firewalls usually implement Application Layer Gateway functionality, which intercepts and analyzes session signaling traffic such as Session Initiation Protocol (SIP) [RFC3261] messages and creates a dynamic mapping to permit the corresponding media traffic. In particular, a firewall extracts media transport addresses, transport protocol and ports from session description and creates a dynamic mapping for media to flow through. This model will not work in the following cases: 1. Session signaling is end-to-end encrypted (say, using TLS). 2. Firewall does not understand the session signaling protocol, or extensions to the protocol, used by the endpoints. 3. Session signaling and media traverse different firewalls (e.g., signaling exits a network via one firewall whereas media exits a network via a different firewall) When an enterprise deploys WebRTC, the above problems are relevant because: 1. Session signaling between WebRTC application running in a browser and a web server will use TLS. 2. WebRTC does not enforce a particular session signaling protocol; therefore, a firewall is unlikely to understand the signaling protocol. Wing, et al. Expires October 4, 2014 [Page 3] Internet-Draft PCP for 3rd party Authorization April 2014 3. Session signaling and peer-to-peer media may traverse different firewalls. As a result firewalls block media traffic. A mitigation to the problems above is for an enterprise to deploy a TURN server in the DMZ and have WebRTC clients use the TURN server. The use-case explained in Section 4.2.5.1 of [I-D.ietf-rtcweb-use-cases-and-requirements] refers to deploying a TURN [RFC5766] server to audit all media sessions from inside the company premises to any external peer. However, using TURN for all such communication causes some problems for an enterprise network administrator : o Enterprise firewalls would typically have granular policies to permit calls initiated using selected WebRTC servers (Dr. Good) it trusts and block the rest (Dr. Evil). o A TURN server just provides a 5-tuple (source IP address, destination IP address, protocol number, source port number, and destination port number) for auditing and no other details of the WebRTC or SIP server being used to establish the call. o A TURN server could increase media latency as explained in section 4.1.2.2 of [RFC5245]. o A TURN server could either be located in the DMZ of the enterprise network or located in the public Internet. If the TURN server is located in the public Internet it comes at a high cost to the provider of the TURN server, since the server typically needs a high-bandwidth connection to the Internet as explained in the Introduction of [RFC5766]. As a consequence, it is best to use a TURN server only when a direct communication path cannot be found. When the client and a peer use ICE to determine communication path, ICE will use hole punching techniques to search for a direct path first and only use a TURN server when a direct path cannot be found. o Other limitations of TURN are explained in section 2.6 of [RFC5766]. For example the value of Diffserv field may not be preserved, Explicit Congestion Notification (ECN) field may be reset etc. Wing, et al. Expires October 4, 2014 [Page 4] Internet-Draft PCP for 3rd party Authorization April 2014 4. Solution Overview In the below topology, the main functional elements involved are : ========================= | WebRTC Server | ========================= | 3rd Party Network | | ================== | WAN |-----+-+----+---+----+-+--- ================== | | | | | | | +-------+-------+ | | Firewall - | | | PCP Server | | +-------+-------+ | | | | | Branch office | | Mobile Network -+-+-----+-----------+-+-----+-------- ----+-+-------+------ | | +-+----------+ +--------+ | Alice - | | Bob | | PCP Client | | | +------------+ +--------+ Users : Alice, Bob WebRTC Server : OAuth 2.0 Authorization server Figure 1: WebRTC server in a different administrative domain In the topology, a WebRTC Server is deployed in a third party network trusted by the Enterprise. For the two endpoints to successfully establish media sessions, a firewall needs to permit ICE [RFC5245] connectivity checks and subsequent media traffic. In such a scenario this specification proposes that a PCP client follows the steps described below: 1. The PCP client makes a PCP request without any authorization. If the PCP server returns an AUTHORIZATION_REQUIRED error message, Wing, et al. Expires October 4, 2014 [Page 5] Internet-Draft PCP for 3rd party Authorization April 2014 the PCP client concludes that the PCP server is mandating the use of third party authorization. 2. The PCP client then obtains a cryptographic token from an OAuth 2.0 Authorization server. 3. The PCP client sends a PCP request including the cryptographic token in the TOKEN_ACCESS option, defined below. Alternatively, the PCP client could first obtain a cryptographic token from the OAuth 2.0 Authorization server and send the PCP request with the TOKEN_ACCESS option by default. 4. The PCP server uses the TOKEN_ACCESS option to perform third party authorization. The technique proposed in the specification can be used by any other Application Function trusted by the network to permit time-bound, encrypted, peer-to-peer traffic. 5. Obtaining a Token Using OAuth This section explains OAuth 2.0 authorization framework [RFC6749] to solve the "Third Party Authorization" requirement explained in section 4 of [I-D.reddy-pcp-auth-req]. The following mapping of OAuth concepts to PCP is used : +----------------------+----------------------------+ | OAuth | PCP | +======================+============================+ | Client | PCP Client | +----------------------+----------------------------+ | Resource owner | Authorization Server. For | | | example the WebRTC server | +----------------------+----------------------------+ | Authorization server | Authorization server. | +----------------------+----------------------------+ | Resource server | PCP Server | +----------------------+----------------------------+ Figure 2: OAuth terminology mapped to PCP terminology Using the OAuth 2.0 authorization framework, a PCP client (third- party application) obtains limited access to a PCP server (resource server) on behalf of the WebRTC server (resource owner or authorization server). The PCP client requests access to resources controlled by the resource owner (WebRTC server) and hosted by the resource server (PCP server). The PCP client obtains an access Wing, et al. Expires October 4, 2014 [Page 6] Internet-Draft PCP for 3rd party Authorization April 2014 token, lifetime, and other access attributes like the PCP options and opcodes that the PCP client is permitted to use from the authorization server. The PCP client conveys the token in the PCP ACESS_TOKEN option to access the protected resources hosted by the resource server (PCP server). The PCP server validates the token and takes appropriate action e.g., allows the PCP request to create mappings on the PCP server. +---------------+ +-------------->| +-------+ | | Authorization | | | +--------| Server | | | | |(WebRTC Server)| | Authorization | | | |<--+ | (e.g Permit MAP/PEER) (1) | | +---------------+ | | (5) Access | | Access | | Token | | Token Get Token | | Request| | (2) Resource | | | | (4) | | | | | | | V | V +-------+---+ +-+----=-----+ | | (3) | | | | PCP Request + Access | | | PCP | Token | PCP | | Client |---------------------->| Server | | (Alice) | PCP Response (6) | (Firewall) | | |<----------------------| | +-----------+ +------------+ User : Alice Figure 3: Interactions OAuth in [RFC6749] defines four grant types. This specification uses the OAuth grant type "Implicit" explained in section 1.3.2 of [RFC6749] where the PCP client is issued an access token directly. The scope of the access token explained in section 3.3 of [RFC6749] MUST be PCP. 5.1. ACCESS_TOKEN Option This specification defines a new PCP ACCESS_TOKEN Option that is described inFigure 4. Wing, et al. Expires October 4, 2014 [Page 7] Internet-Draft PCP for 3rd party Authorization April 2014 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Option Code=TBD| Reserved | Option Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Domain Name Length | Reserved1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Domain Name | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | key id | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | access token length | Reserved3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | access token | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: PCP ACCESS_TOKEN Option The fields are described below: Option Length: 16 bits. Indicates the length of the enclosed data, in octets. Variable, but MUST NOT be 0. Domain Name Length: Length of the 'Domain Name' field in octets. Reserved1: set to 0 by sender and ignored by the receiver. Server Domain Name: The domain name of the Authorized Server that generated the access token. Timestamp: 64-bit unsigned integer field containing a timestamp. The value indicates the time since January 1, 1970, 00:00 UTC, by using a fixed point format. In this format, the integer number of seconds is contained in the first 48 bits of the field, and the remaining 16 bits indicate the number of 1/64K fractions of a second (Native format - Unix). Lifetime: The lifetime of the access token since the response was generated, in seconds. For example, the value 3600 indicates one Wing, et al. Expires October 4, 2014 [Page 8] Internet-Draft PCP for 3rd party Authorization April 2014 hour. The Lifetime value SHOULD be equal to the "expires_in" parameter defined in section 4.2.2 of [RFC6749]. key id: An ephemeral and unique key identifier generated by the authorization server. The authorization server MUST NOT generate the same key identifier twice within the lifetime of the access token. access token length: Length of the access token field in octets. OAuth does not impose any limitation on the length of the access token but since PCP messages cannot exceed 1100 octets (Section 7 of [RFC6887]), access token length needs to be restricted to fit within the maximum PCP message size. The access token is defined in section 1.4 of [RFC6749]. TBD : what is the recommended/ maximum token length for PCP. We need a discussion of this maximum length and analysis of what that means Reserved3: set to 0 by sender and ignored by the receiver. access token: The access token issued by the authorization server. Option Name: ACCESS_TOKEN Number: TBA in the mandatory-to-process range (IANA) Purpose: This option conveys the token granted by the authorization server for third party authorization. Valid for Opcodes: MAP, PEER May appear in : request. Maximum occurrences : 1 5.2. Generating the ACCESS_TOKEN option The mechanism used by an OAuth client to obtain a token from the OAuth authorization server is outside the scope of this document. The OAuth client could obtain the token via in-band signaling or an exclusive out-of-band protocol. This specification uses the token type Handle described in [RFC6819]. A handle token is a reference to some internal data structure within the OAuth authorization server; the internal data structure contains the attributes of the token such as allowed PCP Opcode or PCP Option, etc. The PCP client, after receiving the access token from the OAuth authorization server, generates the ACCESS_TOKEN option which is included in the PCP request to the PCP server. Wing, et al. Expires October 4, 2014 [Page 9] Internet-Draft PCP for 3rd party Authorization April 2014 5.3. PCP server processing ACCESS_TOKEN option A PCP server performs processing in the order described below. When a PCP server receives a PCP request with an ACCESS_TOKEN option, it will verify that the access token is valid. To address replay attacks, the PCP server MUST perform the following check : When a PCP request with an ACCESS_TOKEN Option is received, the received timestamp (TSnew in the Timestamp field) is checked and the cryptographic token is accepted if the timestamp is recent enough to the reception time of the PCP request, RDnew : Lifetime + Delta > abs(RDnew - TSnew) The RECOMMENDED value for the allowed Delta is 5 seconds. If the timestamp is NOT within the boundaries then discard the PCP request with AUTHORIZATION-FAILED error response defined in [I-D.ietf-pcp-authentication]. After the validation described above, the PCP server communicates with the authorization server in order to validate the token and obtain token-bound data. The mechanism for communication is outside the scope of this document. The PCP server makes a request to the authorization server to validate the token but produces no other data with the request. If the token is successfully validated, the authorization server just returns the token bound authorization data in the response. The PCP server then matches this authorization data with what is requested in the PCP request sent by the PCP client. If the authorization sets match, the PCP server honors the PCP request made by the PCP client. If the token is invalid or the request exceeds what is authorized by the token then the PCP server generates an AUTHORIZATION-FAILED error response. An example might be that an OAuth authorization server permits creating 5 mappings, and the PCP request made by the client is trying to create a 6th mapping. Handle token type was selected for the following reasons : 1. The Authorization Server can inform the PCP server to revoke the access token after the call is terminated. This mechanism ensures that even if the PCP client does not close the dynamic mapping created, the PCP server based on the revocation notification from the Authorization Server can close the dynamic mapping. Wing, et al. Expires October 4, 2014 [Page 10] Internet-Draft PCP for 3rd party Authorization April 2014 2. A PCP-controlled Firewall with restrictive policies may also want to validate with the Authorization Server if the selected candidate pairs in the final offer/answer match the 5-tuple {dest addr, source addr, protocol, dest port, source port} sessions traversing the Firewall. This validation ensures that the PCP client is using the token only to send and receive the media streams finalized in the call to the remote peer. Thus the PCP server can make sure that the token cannot be used for anything else. 3. If PCP authentication [I-D.ietf-pcp-authentication] is used then the PCP server may also validate with the authorization server if the access token is issued and used by the same user or not. Another approach, not discussed in this document, is a self-contained token where all the information necessary to authenticate the validity of the token is contained within the token itself. This approach has the benefit of avoiding a protocol between the PCP server and the OAuth authentication server for token validation, thus reducing latency. However, this approach has the drawback of needing a large PCP packet to accommodate the token. Because PCP messages are limited to 1100 octets, using the handle approach is more flexible and the trade-off for additional latency is reasonable. The other disadvantages of self-contained tokens, such as difficulties with revocation etc., are discussed in[RFC6819]. 5.4. Processing the PCP response Upon receiving a PCP response, the PCP client performs the normal processing described in Section 8.3 of [RFC6887]. If the PCP response was SUCCESS (0), the PCP server has determined that the token is valid. If the PCP response was AUTHORIZATION-FAILED, it indicates that the token could be invalid, expired or the PCP request exceeded what is authorized by the token. 6. PCP Server and Proxy behavior The ACCESS_TOKEN option is mandatory-to-process (its most significant bit is clear). Thus, per existing behavior described in [RFC6887], a PCP server receiving this option MUST return the error MALFORMED_OPTION if the option contents are malformed, or UNSUPP_OPTION if the option is unrecognized, unimplemented, or disabled, or if the client is not authorized to use the option. A PCP Proxy MUST follow the rules mentioned in section of 3.4 of [I-D.ietf-pcp-proxy] when processing the ACCESS_TOKEN option. Wing, et al. Expires October 4, 2014 [Page 11] Internet-Draft PCP for 3rd party Authorization April 2014 7. Usage with PCP Authentication mechanism The following steps MUST be followed when PCP third party authorization is used with PCP authentication mechanism. o PCP client MUST send the access token after successful EAP authentication. This provides integrity protection for ACCESS_TOKEN option. o If PCP Auth session lifetime expires before the authorization token expires and the PCP client, PCP server fail to trigger re- authentication then dynamic mappings created because of third party authorization MUST be deleted. 8. Security Considerations Security considerations discussed in [RFC6887] and PCP authentication [I-D.ietf-pcp-authentication] are to be taken into account. If left unprotected the Authorization server could present a means for an attacker to poll a series of possible token values, fishing for a valid token. Therefore, the Authorization Server SHOULD issue special credentials to PCP server to access it and the communication between PCP server and Authorization server MUST be protected using TLS. A PCP server will delete explicit dynamic mappings after the lifetime of the cryptographic token expires. The PCP client must obtain a new cryptographic token from the authorization server before the current token becomes invalid or expires. The PCP client must propagate the new cryptographic token to the PCP server to refresh lifetime of mappings before the current token becomes invalid or expires. The PCP server in addition to timestamp checking can also maintain a cache of used key id as an effective countermeasure against replay attacks. Discussion: If the additional latency needs to be avoided and it is permissible to create a PCP mapping briefly for PCP clients, an implementation could create PCP mappings while the token is being validated. The PCP server could create a mapping immediately, send a PCP response and in parallel start verification of the token. If the verification request times out or returns a failure response, the PCP mapping can be destroyed and a PCP mapping update is sent to the PCP client. The PCP server while waiting for the validation response to arrive from Authorization server can either drop or buffer the traffic matching the mapping created. Wing, et al. Expires October 4, 2014 [Page 12] Internet-Draft PCP for 3rd party Authorization April 2014 9. IANA Considerations We request IANA register the PCP option ACCESS_TOKEN and the result code AUTHORIZATION_REQUIRED in [pcp-registry]. 10. Acknowledgements Authors would like to thank Dave Thaler, Charles Eckel, Paul Jones, Dacheng Zhang, Anca Zamfir, Parthasarathi R and Suresh kumar for their comments and review. 11. References 11.1. Normative References [I-D.ietf-pcp-authentication] Wasserman, M., Hartman, S., and D. Zhang, "Port Control Protocol (PCP) Authentication Mechanism", draft-ietf-pcp- authentication-03 (work in progress), February 2014. [I-D.ietf-pcp-proxy] Perreault, S., Boucadair, M., Penno, R., Wing, D., and S. Cheshire, "Port Control Protocol (PCP) Proxy Function", draft-ietf-pcp-proxy-05 (work in progress), February 2014. [I-D.reddy-pcp-auth-req] Reddy, T., Patil, P., Wing, D., and R. Penno, "PCP Authentication Requirements", draft-reddy-pcp-auth-req-04 (work in progress), July 2013. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session Traversal Utilities for NAT (STUN)", RFC 5389, October 2008. [RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain of Interpretation", RFC 6407, October 2011. [RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC 6749, October 2012. [RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 2013. Wing, et al. Expires October 4, 2014 [Page 13] Internet-Draft PCP for 3rd party Authorization April 2014 [pcp-registry] IANA, , "Port Control Protocol (PCP) Parameters", May 2013, . 11.2. Informative References [I-D.ietf-rtcweb-overview] Alvestrand, H., "Overview: Real Time Protocols for Brower- based Applications", draft-ietf-rtcweb-overview-09 (work in progress), February 2014. [I-D.ietf-rtcweb-use-cases-and-requirements] Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real- Time Communication Use-cases and Requirements", draft- ietf-rtcweb-use-cases-and-requirements-14 (work in progress), February 2014. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, April 2010. [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)", RFC 5766, April 2010. [RFC5853] Hautakorpi, J., Camarillo, G., Penfield, R., Hawrylyshen, A., and M. Bhatia, "Requirements from Session Initiation Protocol (SIP) Session Border Control (SBC) Deployments", RFC 5853, April 2010. [RFC6342] Koodli, R., "Mobile Networks Considerations for IPv6 Deployment", RFC 6342, August 2011. [RFC6819] Lodderstedt, T., McGloin, M., and P. Hunt, "OAuth 2.0 Threat Model and Security Considerations", RFC 6819, January 2013. Wing, et al. Expires October 4, 2014 [Page 14] Internet-Draft PCP for 3rd party Authorization April 2014 Authors' Addresses Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, California 95134 USA Email: dwing@cisco.com Tirumaleswar Reddy Cisco Systems, Inc. Cessna Business Park, Varthur Hobli Sarjapur Marathalli Outer Ring Road Bangalore, Karnataka 560103 India Email: tireddy@cisco.com Prashanth Patil Cisco Systems, Inc. Bangalore India Email: praspati@cisco.com Reinaldo Penno Cisco Systems, Inc. 170 West Tasman Drive San Jose 95134 USA Email: repenno@cisco.com Wing, et al. Expires October 4, 2014 [Page 15]