[Openid-specs-ab] Guidance on what the different flows are for

Mike Jones Michael.Jones at microsoft.com
Wed Oct 30 06:42:01 UTC 2013

"Implicit Flow" is defined in the Terminology section.

From: n-sakimura
Sent: 10/29/2013 9:51 PM
To: openid-specs-ab at lists.openid.net
Subject: Re: [Openid-specs-ab] Guidance on what the different flows are for

(2013/10/30 10:22), Mike Jones wrote:
Several reviewers have requested guidance on when to use the different flows.  I believe that we’d be doing a service to our readers by providing it.

Several reviewers have objected to this text in http://openid.net/specs/openid-connect-core-1_0.html#Authentication – saying that sometimes the Code flow is used even when the client can’t maintain the secrecy of the client_secret:
The Authorization Code Flow is suitable for Clients that can securely maintain a Client Secret between themselves and the Authorization Server whereas, the Implicit Flow is suitable for Clients that cannot.

I believe that that the statement would still be true if we changed the word “suitable” to “intended”.  And then, as discussed in the F2F meeting, we could add the sentence:
“However, the Authorization Code flow is sometimes also used by Native applications in order to be able to obtain a Refresh Token, even when they cannot ensure the secrecy of the client_secret value.”
It does not have to be native applications.
We do not have to constrain code grant for anything.

Only the thing which may be worth noting is that (1) enables client authentication for confidential clients, (2) allows clients to obtain refresh token, (3) more secure than implicit grant as the token is not exposed in the front channel, (4) requires extra roundtrip compaired to the implicit, (5) Token endpoint has to be directly reacheable from the client.

In contrast, the implicit grant will have (1) less roundtrip and thus latency, (2) the client does not need a direct reacheability to the server,  (3) client cannot be confidential, (4) tokens are exposed in the frong channel so inherently less secure, and (5) you cannot get refresh token with this grant.

Perhaps having tables like the following  is better as the guidance.

Conditions / Requirement

code grant

implicit grant

hybrid grant

Server is not directly reachable from the client


Want less round trip



Do not want to reveal tokens for better security



Want client authentication



Want refresh token



Slow front channel, fast back channel



The same table is uploaded here: http://nat.sakimura.org/2013/10/30/guidance-on-which-grant-flow-to-use-for-openid-connect/

BTW, do we still want to use the term "flow"? OAuth stopped using the term and it uses "grant" instead. Currently, "implicit flow" for example is not defined.


Would that combination work for people?

Finally, I propose that we add this guidance about the Hybrid Flow:
“The Hybrid flow enables Clients to obtain an ID Token and/or Access Token with only one round trip to the Authorization Server, possibly minimizing latency, while still enabling Clients to later get tokens from the Token Endpoint – especially a Refresh Token.”

Per the decision at the F2F, all this “guidance” text would move to the introduction.

Are people good with the wording above, or would you like to make alternative suggestions?

                                                                -- Mike

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Nat Sakimura (n-sakimura at nri.co.jp<mailto:n-sakimura at nri.co.jp>)
Nomura Research Institute, Ltd.
Tel:+81-3-6274-1412 Fax:+81-3-6274-1547

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