Question

I have a Facebook canvas iframe application that uses the JavaScript SDK. How do I get the user’s name without them having to authorise the application?

Answer 1

No, it is not possible.

When Facebook calls your page, it’s done by POSTing into an iframe and you get a signed request which lacks most data if the user hasn’t yet to authorize your applications, as it says in the documentation:

Some fields and values, the user_id and oauth_token for example will
only be passed if the user has authorized your app

The Graph API request require you to supply an active access token, otherwise you should get this error:

{
  "error": {
    "message": "An active access token must be used to query information about the current user.", 
    "type": "OAuthException", 
    "code": 2500
  }
}

(You can check that in the Graph API Explorer; just remove the access token before you try.)