FB exchange token api throwing error

I am testing a GET request on a development server to exchange a code for an access token.

Oauth form URL:

https://www.facebook.com/dialog/oauth?
    client_id=1543358959292867%0A&
    redirect_uri=http%3A%2F%2Flocalhost%3A8080%2FFBLoginCallback&
    response_type=code&
    scope=email+user_birthday+user_about_me

Callback w/code.

http://localhost:8080/FBLoginCallback?code=AQAsGssRxA9nDZ2YQ82Dgdw_NB_MsikZxVanO75QG0hKlH9F49v7CEiu5ssBHLmvF_hc4081Q5KcJq9cgC9pyIacz-ekpL6WKv5x0E12-HRzvR7bSImWJMktfTIfbabIDDy3BsOue2GhGos7qlIbU-XJGrzWMehbEhAb4p-2rpd4bVnIqKvaErU2Ma8onUMM8HICyf7IaArOlZs5VYqQDO0IjxsTot5DdU0j8IyBdmtksdspPK-YMhFcJTXabAxO2tWnvOQhAMCH00rlIByCY-xXMIgiLfrnF_YRrs9x5lU2d8ZF2DZrHgXLfnxH1Hh-bGQ#_=_

I get the following response.

oauth2: cannot fetch token: 400 Bad Request
Response: {"error":{"message":"The username for your HTTP Basic Authorization must be 1543358959292867","type":"OAuthException","code":101,"fbtrace_id":"HTJcNHH6OmY"}}

The issue is that this error occurs on one of my two laptops. They both run the exact same code.

This is the golang function I am using for the exchange.

tok, err := fbConfig.Exchange(oauth2.NoContext, r.FormValue("code"))

The error message says that your username for Basic Auth must be 1543358959292867, yet the client_id you provide is actually 1543358959292867\n <- newline tacked on the end (encoded as %0A in your query params).

I don't think the issue is necessarily tied to being different machines, but the input that is being used from those different machines.

A simple thing to do would be log the client_id so you can see what it is when it works and what it is when id doesn't. When you log it you may want to wrap it with a known character so you can see newlines. For example,

fmt.Printf("|%s|", client_id)

If client_id contains a newlines then that will log something like

|1543358959292867
|

instead of

|1543358959292867|

You could also use strings.TrimSpace to remove any prefix or suffix whitespace including newlines.

client_id = strings.TrimSpace(client_id)