Apps got complete access to a user’s account • Users couldn’t revoke access except by changing their password • Compromised apps exposed the user’s password
to obtain an access token • Authorization Code Flow: web apps, native apps • Device Flow: browserless or input-constrained devices • Password: not really OAuth, only for first-party apps • Refresh Token: getting a new access token when it expires
anything where the client cannot keep strings confidential. • Javascript clients: "view source" • Native apps: can decompile and see strings • No secret is used for these clients, only the ID
I’d like to use this great app App: Please go to the authorization server to grant me access User: I’d like to log in to “The Best App Ever”, it wants write access to my account Authz: Here is a temporary code the app can use App: Here is the temporary code, please give me a token User: Here is the temporary code, please use this to get a token Authz: Here is an access token! App: Please let me access this user’s data with this access token!
that your client expects to receive an authorization code • client_id=CLIENT_ID - The client ID you received when you first created the application • redirect_uri=REDIRECT_URI - Indicates the URL to return the user to after authorization is complete, such as https://example-app.com/callback • scope=photos - A space-separated string indicating which parts of the user's account you wish to access • state=1234zyx - A random string generated by your application, which you'll verify later
to the application with an authorization code https://example.com/auth?error=access_denied The user is redirected back to the application with an error code If User Denies
- indicates that this request contains an authorization code • code=CODE_FROM_QUERY - Include the authorization code from the query string of this request • redirect_uri=REDIRECT_URI - This must match the redirect_uri used in the original request • client_id=CLIENT_ID - The client ID you received when you first created the application • client_secret=CLIENT_SECRET - Since this request is made from server-side code, the secret is included
"expires_in":3600, "refresh_token":"64d049f8b21191e12522d5d96d5641af5e8" } The server replies with an access token and expiration time or if there was an error: {"error":"invalid_request"}
Server accounts.google.com Yes No Allow Example App to access your public profile and contacts? example-app.com/callback Loading… Direct the user to the authorization server response_type=code &redirect_uri=example-app.com/callback &state=00000 User signs in Authorization server redirects back to the app code=XYZ123&state=00000 Exchange authorization code for an access token
that your client expects to receive an access token • client_id=CLIENT_ID - The client ID you received when you first created the application • redirect_uri=REDIRECT_URI - Indicates the URI to return the user to after authorization is complete, such as https://example-app.com/callback • scope=photos - A space-separated string indicating which parts of the user's account you wish to access • state=1234zyx - A random string generated by your application, which you'll verify later
a "code verifier", a random string 43-128 characters long. • Compute the SHA256 hash of the code verifier, call that the code challenge • Include code_challenge=XXXXXX and code_challenge_method=S256 in the initial authorization request • Send the code verifier when exchanging the authorization code for an access token • (For clients that can't support SHA256, include the plaintext verifier as the challenge, and set the method to "plain")
43-128 characters long ipSBt30y48l401NGbLjo026cqwsRQzR5KI40AuLAdZ8 The challenge is the SHA256 hash of the verifier string base64url(sha256(code_verifier)) Generate the Code Challenge
to the application with an authorization code example://auth?error=access_denied The user is redirected back to the application with an error code If User Denies
then make a POST request: • grant_type=authorization_code - indicates that this request contains an authorization code • code=CODE_FROM_QUERY - Include the authorization code from the query string of this request • redirect_uri=REDIRECT_URI - This must match the redirect_uri used in the original request • client_id=CLIENT_ID - The client ID you received when you first created the application • code_verifier=VERIFIER_STRING - The plaintext code verifier initially created
grant_type=authorization_code& code=AUTH_CODE_HERE& redirect_uri=REDIRECT_URI& client_id=CLIENT_ID& code_verifier=VERIFIER_STRING Note: code verifier used in place of client secret
"expires_in":3600", "refresh_token":"64d049f8b2119a12522d5dd96d5641af5e8" } The server compares the code_verifier with the code_challenge that was in the request when it generated the authorization code, and responds with an access token.
https://api.authorization-server.com/token grant_type=password& username=USERNAME& password=PASSWORD& client_id=CLIENT_ID& client_secret=CLIENT_SECRET The user’s credentials are sent directly! Not a good idea for third party apps!
POST https://api.authorization-server.com/token grant_type=client_credentials& client_id=CLIENT_ID& client_secret=CLIENT_SECRET No user context in the request, so the access token can only be used to access the application’s resources
Request a Device Code { "device_code": "NGU5OWFiNjQ5YmQwNGY3YTdmZTEyNzQ3YzQ1YSA", "user_code": "BDWD-HQPK", "verification_uri": "https://example.com/device", "interval": 5, "expires_in": 1800 } The server responds with a new device code and user code, as well as the URL the user should visit to enter the code.
waits for the user to enter the code and authorize the application, the device polls the token endpoint. { "access_token": "RsT5OjbzRn430zqMLgV3Ia", "expires_in": 3600, "refresh_token": "b7aab35e97298a060e0ede5b43ed1f70a8" }
used to get new access tokens • Requested along with the id_token or access token in the initial step • Usually requires scope: offline_access • Usually not issued to Javascript apps
Defining Scopes !89 • Read / Write • Restrict access to sensitive information • e.g. private repos on GitHub • By functionality • e.g. Google Drive, YouTube, Gmail • Billable resources
Presenting Scopes to the User !90 • Provide clear and straightforward information • Provide enough detail so the user knows what the application can access • Don't provide too much detail that they are overwhelmed and just click "ok"
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