OpenIDConnect Response Type Confusion

Question

I've spend the last few days reading through all the specs with regards to OAuth2 and OpenIDConnect and implementing a test client using Thinktecture Identity Server. I've also followed several pluralsight courses and I think understand the main gist of it. However i'm still extremely confused about the Response Types.

OpenIDConnect spec specifies that the Hybrid flow response types are a combination of "code", "id_token" and "token". I understand the "id_token" allows us to get access to basic id information initially.

I also understand code" refers to the authorization code and "token" refers to an access token and combining "code" with one or both of the other two triggers the flow but my understanding was that you swap an authorization code for an access token in the Authorization flow, while the Implicit flow supplies the Access Code implicitly?

Could someone clear up my confusion?

Answer 1

The following statements that you made are correct:

• code refers to the Authorization Code
• token refers to an Access Token or (access_token)
• in the Authorization Code flow one switches the code for an access_token

But part of your confusion may originate from terminology mixup:

• the term Authorization flow is not entirely correct; its official name is Authorization Code flow
• the term Access Code does not exist
• the Implicit flow does not have an Authorization Code (nor Access code) in fact there's no credential (or grant) involved at all that allows the Client to get tokens from the Token endpoint, hence it's name

As @juanifioren pointed out, Hybrid flows combine things:

• the code id_token flow would get a code and id_token in the Authentication Response directly but you'd use the code to get an access_token from the Token endpoint
• the code token flow would get a code and access_token in the Authentication Response directly but you'd use the code to get an id_token and possibly another access_token in the backend from the Token endpoint
• the code id_token token flow would get a code, access_token and an id_token in the Authentication Response directly and you could use the code in the backend to get another access_token from the Token endpoint

Getting an access_token from the Token endpoint differs from getting it from the Authorization endpoint because the confidential clients authenticate themselves to the Token endpoint (and not to the Authorization endpoint). Hence the access_token for the confidential part of the client might have more permissions and or a longer life.

See also a short thread on the spec mailing list on this topic: http://lists.openid.net/pipermail/openid-specs-ab/Week-of-Mon-20150209/005229.html

Answer 2

To understand the possible relationships between Response Types and Grant Types see IdentityServer4\Constants.cs

public static readonly Dictionary<string, string> ResponseTypeToGrantTypeMapping = new Dictionary<string, string>
        {
            { OidcConstants.ResponseTypes.Code, GrantType.AuthorizationCode },
            { OidcConstants.ResponseTypes.Token, GrantType.Implicit },
            { OidcConstants.ResponseTypes.IdToken, GrantType.Implicit },
            { OidcConstants.ResponseTypes.IdTokenToken, GrantType.Implicit },
            { OidcConstants.ResponseTypes.CodeIdToken, GrantType.Hybrid },
            { OidcConstants.ResponseTypes.CodeToken, GrantType.Hybrid },
            { OidcConstants.ResponseTypes.CodeIdTokenToken, GrantType.Hybrid }
        };