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> > In my experience with OAuth, one of the principle issues is that it's less a protocol and more a skeleton of a protocol > OAuth supports lots of different

> > In my experience with OAuth, one of the principle issues is that it's less a protocol and more a skeleton of a protocol > OAuth supports lots of different scenarios. But it's literally only the skeleton of a protocol ("framework" of a protocol, as the actual spec puts it). That important "Then later on you can take the token and say 'Hey google, somebody gave me this token, who is it?'" part is totally unspecified by OAuth. How do you validate tokens? (Either on the resource-server end, or on the client-end to know if trying to talk to a resource-server is a waste of time, or to know if your post-redirect-uri is getting spoofed): - OAuth: implementation defined - most implementations: use our library, which validates the token using undocumented logic - OIDC: there's a user-info endpoint you can call to, but lots of OAuth authorization servers don't fully implement OIDC, and even if they do, that's a lot of extra round trips - RFC7523: The token is a JWT, validate the signature and claims... but everyone issues RFC6750 "bearer" tokens, not RFC7523 "urn:ietf:params:oauth:grant-type:jwt-bearer" tokens. But if you just close your eyes and pretend that your 6750 opaque token is actually a 7523 JWT and parse+validate it as such, that'll work most of the time. So yeah, OAuth is hard because there's no great generic library, because a core part of it is implementation-defined, so you have to either do it yourself or use a specific implementation's library, and none of those libraries work quite the same. (In the above, and for 99% of folks, "OAuth" = RFC6749+RFC6750)

rtpg 3y ago
In all honesty, though, "I have to look at the provider's documentation to determine like 4 URLs to add to a configuration" is not that wild of a thing? How much friction is too much friction? > How do you validate tokens? (Either on the resource-server end, or on the client-end to know if trying to talk to a resource-server is a waste of time, or to know if your post-redirect-uri is getting spoofed): At the beginning of the "standard" OAuth flow you can pass in client state. So you generate a signed nonce. Remember, you are starting this flow, so you mix in some user data (avoids CSRF problems), and you are pointing to some HTTPS site. This is not 100% perfect compared to "remote server has some signing" but it does allow purely local verification of tokens when they are first received, as you can stick stuff into the "state" request parameter (as anyone should be anyways to avoid trickery).
- LukeShu 3y ago
  > In all honesty, though, "I have to look at the provider's documentation to determine like 4 URLs to add to a configuration" is not that wild of a thing? How much friction is too much friction? If it's something dumb/simple like grabbing a JWKS URL and an "issuer" URL, and then doing JWT validation, sure. Maybe you need to make a weird bespoke request to some other endpoint. Maybe you need to implement some uncommon signature verification. It could be anything. > At the beginning of the "standard" OAuth flow you can pass in client state. So you generate a signed nonce. Remember, you are starting this flow, so you mix in some user data (avoids CSRF problems), and you are pointing to some HTTPS site. So you redirect the user's browser to the IDP, with the nonce in the URL. The user grabs that nonce from the URL bar, then manually navigates to your redirection-endpoint, putting that nonce and their own fabricated token in the URL.
  - krinchan 3y ago
    ...what? The server generates the auth code and redirects the user agent to your callback. You exchange that code with the IDP (over HTTPS which yeah that's its own nest of wormy trust) to get back a token. They can't inject a token because you don't get the token from them, just the one time code. If it's opaque you introspect it to validate or you just validate the JWT signature after pulling the keys from the JWKS endpoint. Introspection is standardized and an RFC. The state param is just a fucking session identifier. All these URLs are defined and provided via the .well-known/openid-configuration endpoint. If your IDP publishes that endpoint correctly, most OAuth2 client libraries Just Work (TM) when pointed at the IDP domain. Do EITHER of you even use OAuth2 outside of just cargo culting something you found off GitHub?
    - rtpg 3y ago
      Oh, thank you for reminding me of the well-known endpoint, was having trouble finding it in the OAuth RFCs but I wonder if it's pulled in elsewhere. > They can't inject a token because you don't get the token from them, just the one time code. that's not correct in the most common flow? The most common flow involves the user agent providing the information via a GET, so they can theoretically provide a token. The reason the state parameter is important is because without it, a malicious actor can make a link that goes directly to your system's "oauth step finalized" step, but with their credentials. (Pedantic attack: service has slack push notifications integration, through OAuth. Attacker creates link like https : //service/connect-slack-finalize?token=token-to-attackers-slack that victim clicks on. Without using state, the service will just take the token and stick it into some slack integration. now attacker's slack is getting messages for the victim's account on the service. Cookies mean that the victim's thing is accepted immediately).
TheRealDunkirk 3y ago
Yikes. As someone who is going to need to integrate OAuth using JWT into a Rails app to access an API in the nearish future... I now dread it.

rtpg 3y ago

In all honesty, though, "I have to look at the provider's documentation to determine like 4 URLs to add to a configuration" is not that wild of a thing? How much friction is too much friction? > How do you validate tokens? (Either on the resource-server end, or on the client-end to know if trying to talk to a resource-server is a waste of time, or to know if your post-redirect-uri is getting spoofed): At the beginning of the "standard" OAuth flow you can pass in client state. So you generate a signed nonce. Remember, you are starting this flow, so you mix in some user data (avoids CSRF problems), and you are pointing to some HTTPS site. This is not 100% perfect compared to "remote server has some signing" but it does allow purely local verification of tokens when they are first received, as you can stick stuff into the "state" request parameter (as anyone should be anyways to avoid trickery).

LukeShu 3y ago
> In all honesty, though, "I have to look at the provider's documentation to determine like 4 URLs to add to a configuration" is not that wild of a thing? How much friction is too much friction? If it's something dumb/simple like grabbing a JWKS URL and an "issuer" URL, and then doing JWT validation, sure. Maybe you need to make a weird bespoke request to some other endpoint. Maybe you need to implement some uncommon signature verification. It could be anything. > At the beginning of the "standard" OAuth flow you can pass in client state. So you generate a signed nonce. Remember, you are starting this flow, so you mix in some user data (avoids CSRF problems), and you are pointing to some HTTPS site. So you redirect the user's browser to the IDP, with the nonce in the URL. The user grabs that nonce from the URL bar, then manually navigates to your redirection-endpoint, putting that nonce and their own fabricated token in the URL.
- krinchan 3y ago
  ...what? The server generates the auth code and redirects the user agent to your callback. You exchange that code with the IDP (over HTTPS which yeah that's its own nest of wormy trust) to get back a token. They can't inject a token because you don't get the token from them, just the one time code. If it's opaque you introspect it to validate or you just validate the JWT signature after pulling the keys from the JWKS endpoint. Introspection is standardized and an RFC. The state param is just a fucking session identifier. All these URLs are defined and provided via the .well-known/openid-configuration endpoint. If your IDP publishes that endpoint correctly, most OAuth2 client libraries Just Work (TM) when pointed at the IDP domain. Do EITHER of you even use OAuth2 outside of just cargo culting something you found off GitHub?
  - rtpg 3y ago
    Oh, thank you for reminding me of the well-known endpoint, was having trouble finding it in the OAuth RFCs but I wonder if it's pulled in elsewhere. > They can't inject a token because you don't get the token from them, just the one time code. that's not correct in the most common flow? The most common flow involves the user agent providing the information via a GET, so they can theoretically provide a token. The reason the state parameter is important is because without it, a malicious actor can make a link that goes directly to your system's "oauth step finalized" step, but with their credentials. (Pedantic attack: service has slack push notifications integration, through OAuth. Attacker creates link like https : //service/connect-slack-finalize?token=token-to-attackers-slack that victim clicks on. Without using state, the service will just take the token and stick it into some slack integration. now attacker's slack is getting messages for the victim's account on the service. Cookies mean that the victim's thing is accepted immediately).

TheRealDunkirk 3y ago

Yikes. As someone who is going to need to integrate OAuth using JWT into a Rails app to access an API in the nearish future... I now dread it.