> Rejecting a GET with code in the URL means that the code is never "used" at the AS, so can still be exchanged for an access token; and rejecting the request does not mean it won't leak
That's a good point Thomas. I still think secure OAuth workflows should totally avoid putting any kind of sensitive data in URI's for any step, including POST /Actions/ that leak like a GET query parameter. > So reject if you like from the user's point of view, but "consume" the code anyway (and then immediately revoke the token, maybe), or you're probably making things worse Interesting point, but I think if the standard reflected this suggestion it would be less likely that implementer will do it. > (if you're worried of leaking 5min one-time codes, particularly when that > code cannot be used without a client_secret and/or PKCE code_verifier) Also a good point. This specific step in the workflow might not be at risk as much as other steps, but I see a LOT of folks putting sensitive data in tokens and I'm trying to help avoid that leakage. Thanks for your feedback. Aloha, Jim On 8/13/17 11:20 AM, Thomas Broyer wrote: > Rejecting a GET with code in the URL means that the code is never > "used" at the AS, so can still be exchanged for an access token; and > rejecting the request does not mean it won't leak. So reject if you > like from the user's point of view, but "consume" the code anyway (and > then immediately revoke the token, maybe), or you're probably making > things worse (if you're worried of leaking 5min one-time codes, > particularly when that code cannot be used without a client_secret > and/or PKCE code_verifier) > > Disclaimer: not a security expert here. > > Le sam. 12 août 2017 16:55, Jim Manico <[email protected] > <mailto:[email protected]>> a écrit : > > > The _*safest*_ thing for a client is to accept both. > > I politely (and strongly) disagree with this statement. The safest > thing for a client is to only accept POST or other verbs where any > kind of sensitive data is NOT kept in the URL. Sensitive data in > URL's leak like a sieve, even over HTTPS. > > Respectfully, > Jim > > > > On 8/11/17 3:18 PM, John Bradley wrote: >> OpenID Connect formally defined a POST response mode. >> >> http://openid.net/specs/oauth-v2-form-post-response-mode-1_0.html >> >> The OAuth 2 spec docent preclude it. >> >> The safest thing for a client is to accept both. >> The main advantages of POST is that it docent leak in the >> referrer, and can handle larger responses without the browser >> choking in some cases. >> >> Size is more of an issue in Connect where a id_token may be >> returned in the front channel and POST allows for the larger >> response without the client needing to have JS extract the fragment. >> >> That is why Connect defined it and OAuth largely assumes that for >> code get is OK. >> For security GET responses should add headers to prevent referrer >> from leaking the code. >> >> We are adding advice on that to the Security document that is >> being updated now. >> >> John B. >> >> >>> On Aug 11, 2017, at 4:08 PM, Josh Mandel <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> Fixing my "with this technique" url: it should have been >>> https://gist.github.com/jmandel/4704d1efed8578a67a6f9b600ffd0c63 . >>> >>> On Fri, Aug 11, 2017 at 4:00 PM, Josh Mandel <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> Hi All, >>> >>> I've just encountered a server that performs a redirect >>> (back to the client's redirect_uri) via POST instead of GET. >>> This was surprising behavior to me and broke my client >>> implementation — but citing chapter and verse, the server >>> developer pointed out >>> that https://tools.ietf.org/html/rfc6749#section-1.7 says >>> >>> While the examples in this specification show the use of >>> the HTTP 302 status code, any other method available via >>> the user-agent to accomplish this redirection is allowed >>> and is considered to be an implementation detail. >>> >>> >>> Is triggering a POST-based redirect (e.g. with this >>> technique >>> >>> <https://gist.github.com/jmandel/4704d1efed8578a67a6f9b600ffd0c63%29>) >>> to the redirect_url (including url query parameters for >>> state and code) indeed considered a "method available via >>> the user-agent to accomplish this redirection"? In other >>> words, should a well-behaved OAuth client be prepared to >>> receive GETs as well as POSTs to its redirect_uri? If so, >>> what would be the considerations for a server choosing >>> between GET and POST? >>> >>> Best, >>> >>> Josh >>> >>> >>> _______________________________________________ >>> OAuth mailing list >>> [email protected] <mailto:[email protected]> >>> https://www.ietf.org/mailman/listinfo/oauth >> >> >> >> _______________________________________________ >> OAuth mailing list >> [email protected] <mailto:[email protected]> >> https://www.ietf.org/mailman/listinfo/oauth > > -- > Jim Manico > Manicode Security > https://www.manicode.com > > _______________________________________________ > OAuth mailing list > [email protected] <mailto:[email protected]> > https://www.ietf.org/mailman/listinfo/oauth > -- Jim Manico Manicode Security https://www.manicode.com
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