The 3rd-Generation Partnership Project (3GPP) has defined how the WebRTC framework can be used to provide access to IMS services. Users can use "web credentials" (e.g. a username and password) to retrieve an authorization token (e.g. an OAuth 2.0 access token), which is included in the user registration request sent towards the IMS network. 3GPP has specified a requirement, that the eP-CSCF shall be able to include a string value, representing the identity of the WAF, in the REGISTER request forwarded towards the S-CSCF. The S-CSCF can use the identity for e.g. policy and routing decisions. This document defines a new Authorization header field parameter, 'authorization-entity', which the eP-CSCF can include in a REGISTER request in order to convey the identity of the WAF towards the S-CSCF.