Facebook Messenger Account Linking, How To Use It?

There are 4 easy steps described in the documentation about account linking for the messenger platform: Register a callback URL using Log In Button. Messenger Platform invokes t

Solution 1:

Just been through a similar bit of head scratching, so will explain what I've done while it's fresh in my head

For my example, I wanted Facebook to redirect out to my main login page, which is an open id connect implementation. The customer signs in to this, and I get an id_token and access_token back from that. Upon receiving the access_token, I'm extracting the 'sub' claim from the JWT, which is the unique customer identifier in our database.

I'm then redirecting back to the value that was sent to me in redirect_uri, appending authorization_code={the-value-of-the-sub-claim}

This then triggers the 'account link' webhook, which will Post to my service code, containing the PSID of the Facebook user and the authorization_code, which is my unique customer id in my business database.

You now have the 2 bits of information you need, the unique facebook id and your unique customer id in the Post message. It's up to your business code to persist this information to some sort of storage at this point

On subsequent message posts to the Bot endpoint, you always have the sender (PSID) in the message. Your code can now look up the corresponding id specific to your business and perform operations relevant for that id.

Where the linking takes place - that's in your code, you need to handle the message from the account link webhook and store the data for future use.