Metadata discovery for third party authorized TURN session
draft-reddy-tram-token-metadata-00

Abstract

The operator of the TURN server might want to have fine grained control on the clients usage of the server resources for providing features such as limiting the bandwith usage, number of allocations and so on. This document proposes a generic mechanism for the operator to introspect the access token to retrieve any policy restrictions imposed by the authorization server on the TURN server resources assigned to the client.

Status of This Memo

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This Internet-Draft will expire on February 29, 2016.

Copyright Notice

Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Introspection Request
• 4. Introspection Response
• 5. INTROSPECTION_ENDPOINT Attribute
• 6. Notifications from Introspection Endpoint
• 7. Alternate approach
• 8. Security Considerations
• 9. IANA Considerations
• 9.1. JSON Web Token Claims
• 9.2. Well-Known 'introspection' URI
• 9.3. STUN attribute
• 10. Acknowledgements
• 11. References
• 11.1. Normative References
• 11.2. Informative References
• Authors' Addresses

1. Introduction

The TURN protocol [RFC5766] is used to setup a relay service (via a TURN Server) to exchange traffic (real time media, data) between peers when direct peer-to-peer connection is not otherwise possible. Due to the costs associated with operating a relay service, it is important to constrain resource usage. For example, the operator might want to limit the number of allocations or bandwidth.

[I-D.ietf-tram-turn-third-party-authz] allows clients to obtain OAuth2.0 access token (of type ‘Assertion’) authorized by a Authorization Server to access a given TURN server. On receiving such a token, the TURN server validates the token to grant or reject access to the session resources. However, having a token doesn't provide any control for the operator of the TURN server restrict the server's resources. This specification proposes using the mechanism defined in [I-D.ietf-oauth-introspection] to query OAuth2.0 authorization server to determine resource restrictions for this token.

The rest of the document is organized as follows. Section 3 provides procedure for querying the OAuth2.0 introspection endpoint and Section 4 shows the introspection response with the parameters identifying the policy controls associated with the access token.

2. Terminology

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].

This document defines the following terms:

Access Token: OAuth 2.0 access token.

Token Introspection: The act of inquiring about the current state of an OAuth 2.0 token through use of the network protocol defined in this document.

Introspection Endpoint: The OAuth 2.0 endpoint through which the token introspection operation is accomplished. The Introspection Endpoint could be a WebRTC server.

3. Introspection Request

For introspecting the meta-information associated with the access token, the TURN server shall execute the procedures defined in Section 2.1 of [I-D.ietf-oauth-introspection].

  POST {scheme}://{host}:{port}/.well-known/introspection
  Accept: application/json
  Content-Type: application/x-www-form-urlencoded

  {
      "token" : "string" 
      "token_type_hint" : "string"
  }

token REQUIRED. This parameter is defined in [I-D.ietf-oauth-introspection]. The access token is conveyed by the TURN client to the TURN server as discussed in Section 3.1 of [I-D.ietf-tram-turn-third-party-authz].

token_type_hint OPTIONAL. This parameter is defined in [I-D.ietf-oauth-introspection]. The token type MUST be set to ‘access_token’ defined in [RFC7009]. If the token type is not ‘access_token’, the server rejects the request with a 400 (Bad Request) error.

Following is a non-normative example request showcasing the introspection request for a given access token.

  POST /introspect HTTP/1.1
  Host: server.example.com
  Accept: application/json
  Content-Type: application/x-www-form-urlencoded
  
  {

     "token" : "2YotnFZFEjr1zCsicMWpAA"
     "token_type_hint" : "access_token"

  }

4. Introspection Response

The OAuth2.0 Introspection Endpoint on recognizing the token, responds with a JSON object [RFC7159] in “application/json” format with the following members.

  HTTP/1.1 200 OK
  Content-Type: application/json
 
  {
  "active" : "boolean",
  "scope" : "string",
  "max_upstream_bandwidth" : "unsigned integer",
  "max_downstream_bandwidth" : "unsigned integer",
  "max_allocations" : "unsigned integer",
  "lifetime" : "unsigned integer",
  }

active REQUIRED. This parameter is defined in [I-D.ietf-oauth-introspection].

scope OPTIONAL. This parameter is defined in [I-D.ietf-oauth-introspection]. For this specification, the scope MUST be 'stun'.

max_upstream_bandwidth REQUIRED. The value of this parameter is an 64 bit unsigned integer that represents the maximum upstream bandwidth permitted for the token in kilobits per second (1 kilobit = 1024 bits).

max_downstream bandwidth REQUIRED. The value of this parameter is an 64 bit unsigned integer that represents the maximum downstream bandwidth permitted for the token in kilobits per second (1 kilobit = 1024 bits).

max_allocations: REQUIRED. 16 bit unsigned integer defining maximum number of allocations that is allowable for the given access token.

lifetime: REQUIRED: The lifetime of the access token, in seconds.

NOTE: Future specifications are allowed to define further top-level members as mandated by the use-cases.

Following is a non-normative example response:

  HTTP/1.1 200 OK
  Content-Type: application/json

  {
  "active" : true,
  "scope" : "stun",
  "upstream-bandwidth" : 4096,
  "downstream-bandwidth" : 4096,
  "max-allocations" : 1,
  }

5. INTROSPECTION_ENDPOINT Attribute

This attribute is used by the TURN client to inform the TURN server the FQDN of Introspection Endpoint.

The TURN server establishes an HTTPS connection with the indicated server and sends the above-described communications to that server. The INTROSPECTION_ENDPOINT attribute is a comprehension-optional attribute (see Section 15 from [RFC5389]).

TBD: An alternate approach is to convey the FQDN in the token itself.

6. Notifications from Introspection Endpoint

Introspection Endpoint can send unsolicited responses to notify updates to the metadata associated with the token to the TURN server using HTTP/2 server push mechanism. Examples where such notifications are desired are:

• The Introspection Endpoint can signal the TURN server to revoke the access token after the call is terminated by setting lifetime to zero.
• When the call switches from audio to video, the Introspection Endpoint notifies the increased bandwidth to the TURN server.

7. Alternate approach

TBD:

Another approach, not discussed in this document, is a self- contained token where the metadata is contained within the token itself. This approach has the benefit of avoiding a protocol between the TURN server and the Introspection Endpoint. However, this approach has the following drawbacks:

• Needs a large TURN packet to accommodate the token.
• Token needs versioning for future enhancements, and the Introspection Endpoint needs a mechanism to learn the token version supported by the TURN server.
• Introspection Endpoint cannot notify changes to the metadata associated with the token to the TURN server.

8. Security Considerations

The Security Considerations and Privacy Considerations of [I-D.ietf-oauth-introspection] apply to this document.

9. IANA Considerations

9.1. JSON Web Token Claims

This specification requests IANA to register the following values into the IANA JSON Web Token Claims registry for JWT Claim Names.

• Claim Name: max_upstream_bandwidth
• Claim Description: Maximum limit of upstream bandwidth
• Change Controller: IESG
• Specification Document(s): Section 4 of [[ this document ]].

• Claim Name: max_downstream_bandwidth
• Claim Description: Maximum limit of downstream bandwidth
• Change Controller: IESG
• Specification Document(s): Section 4 of [[ this document ]].

• Claim Name: max_allocations
• Claim Description: Maximum number of allocations
• Change Controller: IESG
• Specification Document(s): Section 4 of [[ this document ]].

9.2. Well-Known 'introspection' URI

This memo registers the 'introspection' well-known URI in the Well-Known URIs registry as defined by [RFC5785].

URI suffix: introspection

Change controller: IETF

Specification document(s): This document

Related information: None

9.3. STUN attribute

[Paragraphs below in braces should be removed by the RFC Editor upon publication]

[IANA is requested to add the following attributes to the STUN attribute registry [iana-stun], the INTROSPECTION_ENDPOINT attribute requires that IANA allocate a value in the "STUN attributes Registry" from the comprehension-optional range (0x8000-0xBFFF)].

This document defines the INTROSPECTION_ENDPOINT attribute, described in Section 5. IANA has allocated the comprehension-optional codepoint TBD for this attribute.

10. Acknowledgements

TODO

11. References

11.1. Normative References

11.2. Informative References

Authors' Addresses