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

n-sakimura n-sakimura at nri.co.jp
Wed Oct 30 04:51:13 UTC 2013


(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

	

	

x

	

Want less round trip

	

	

x

	

x

Do not want to reveal tokens for better security

	

x

	

	

(some)

Want client authentication

	

x

	

	

x

Want refresh token

	

x

	

	

x

Slow front channel, fast back channel

	

x

	

	

x


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.

Nat


> 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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> Openid-specs-ab at lists.openid.net
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-- 
Nat Sakimura (n-sakimura at nri.co.jp)
Nomura Research Institute, Ltd.
Tel:+81-3-6274-1412 Fax:+81-3-6274-1547

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