Sender Constrained Token

Full Title or Meme

A Sender Constrained Token can be considered to be a token there the Subject presenting the token can prove possession of some credential that is bound to the token.

Context

• In common OpenID Connect code flows, the response to the user's consent is used by the relying party (confusingly called the user's client) to request an access_token (which is typically a Bearer Token) and a refresh_token (which is typically a Sender Constrained Token.

Problems

• Bearer Tokens have proven to be susceptible to reuse by unauthorized parties.
• The most commonly accessed protected resource is User Private Information, which has had low value in the view of the web sites heretofore.

Solutions

• Add a cryptographic binding between the token a some credential that is known to be in the secured possession of the Subject]
• For any scenario where the protect resource has high value, a Sender Constrained Token is the more secure solution.