Re: [OAUTH-WG] Confusion on Implicit Grant flow

John Bradley <ve7jtb@ve7jtb.com> Fri, 06 February 2015 21:37 UTC

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From: John Bradley <ve7jtb@ve7jtb.com>
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Date: Fri, 6 Feb 2015 18:37:39 -0300
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To: Adam Lewis <Adam.Lewis@motorolasolutions.com>
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Cc: OAuth WG <oauth@ietf.org>
Subject: Re: [OAUTH-WG] Confusion on Implicit Grant flow
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It isn’t an extra step,  the call back via 302 has to be to a URI in the location header.  The JS loaded by that URI may already be cached in the browser as part of the APP.

The cached JS typically extracts the token and uses it.  The token is never passed to the server where the JS is loaded from. (yes it could be, but if your are doing that then use code or hybrid code+token)

Ther are other ways that could be done using pure Java Script cross origin messaging eg post-message.   However though some people (Google and others) do use that in there custom integrations, a standard for that has not been established.
(there are some real security issues around post message that need to be considered first)

John B.


> On Feb 6, 2015, at 6:27 PM, Adam Lewis <Adam.Lewis@motorolasolutions.com> wrote:
> 
> Hi,
>  
> Having spent most of my time with native apps and web apps, I now am looking at use cases where I need to implement a user-agent-based app.  The Implicit flow seems to be optimized for this.
>  
> To test my understanding, this flow is for a JavaScript client (or similar) executing within a web browser.
>  
> At step (a) the client directs the UA to the authorization server, but the authorization server redirects the UA to a web-hosted client resource.  Why?  It says so that the web-hosted client resources can push javascript (or other) back into the UA so it can extract the access token in the fragment; but some sort of javascript is already running in the browser, since it initiated the authorization request in the first place.  So why this extra step?  Why not treat the javascript client running in the UA like a native app and handle the redirect uri?
>  
> I know this was well thought out when the spec was written, so trying to figure out what I’m missing?
>  
>  
>  
> Tx!
> adam
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