From what you describe I’d suggest to use a server-side login flow as described in
- https://developers.facebook.com/docs/facebook-login/manually-build-a-login-flow/v2.2
so that the token is already on your server, and doesn’t need to be passed from the client. If you’re using non-encrypted connections, this could be a security risk (e.g. for man-in-the-middle attacks).
The steps would be:
(1) Logging people in
You need to specify the permission you want to gather from the users in the scope parameter. The request can be triggered just via a normal link:
GET https://www.facebook.com/dialog/oauth?
client_id={app-id}
&redirect_uri={redirect-uri}
&response_type=code
&scope={permission_list}
See
- https://developers.facebook.com/docs/facebook-login/manually-build-a-login-flow/v2.2#login
(2) Confirm the identitity
GET https://graph.facebook.com/oauth/access_token?
client_id={app-id}
&redirect_uri={redirect-uri}
&client_secret={app-secret}
&code={code-parameter}
- https://developers.facebook.com/docs/facebook-login/manually-build-a-login-flow/v2.2#confirm
(3) Inspect the access token
You can inspect the token as you already said in your question via
GET /debug_token?input_token={token-to-inspect}
&access_token={app-token-or-admin-token}
This should only be done server-side, because otherwise you’d make you app access token visible to end users (not a good idea!).
See
- https://developers.facebook.com/docs/facebook-login/manually-build-a-login-flow/v2.2#checktoken
(4) Extending the access token
Once you got the (short-lived) token, you can do a call to extend the token as described in
- https://developers.facebook.com/docs/facebook-login/access-tokens#extending
like the following:
GET /oauth/access_token?grant_type=fb_exchange_token
&client_id={app-id}
&client_secret={app-secret}
&fb_exchange_token={short-lived-token}
(5) Storing of access tokens
Concerning the storing of the tokens on the server, FB suggests to do so:
- https://developers.facebook.com/docs/facebook-login/manually-build-a-login-flow/v2.2#token
(6) Handling expired access tokens
As FB doesn’t notify you if a token has expired (and if you don’t save the expiry date and compare this to the current timestamp before making a call), it’s possible that you receive error messages from FB if the token got invalid (after max. 60 days). The error code will be 190:
{
"error": {
"message": "Error validating access token: Session has expired at unix
time SOME_TIME. The current unix time is SOME_TIME.",
"type": "OAuthException",
"code": 190
}
}
See
- https://developers.facebook.com/docs/facebook-login/access-tokens#expiredtokens
If the access token becomes invalid, the solution is to have the person log in again, at which point you will be able to make API calls on their behalf once more. The login flow your app uses for new people should determine which method you need to adopt.