Receiving “redirect_uri does not match the uri used to create the passed code”, when it does match

Question

Summary

Using Oauth2, when I go to pick up the access_token, I get the following error from the server: access_denied: redirect_uri does not match the uri used to create the passed code. From what I can tell, the redirect_uri does match the one sent in the oauth request.

Details

Request to the oauth service:

https://stackexchange.com/oauth?client_id=218&redirect_uri=http%3A%2F%2Fwww.noverse.com%2FOAuthStackExchangeCallback&response_type=code

After logging in and authorizing, post_data in the request to the https://stackexchange.com/oauth/access_token service:

client_id=218&client_secret=n%29T7dAbutd0qDKp92ZwwMw%28%28&code=P%2AS4ZqH0gewVi8stHPAqlw%29%29&grant_type=authorization_code&redirect_uri=http%3A%2F%2Fwww.noverse.com%2FOAuthStackExchangeCallback

The response is an HTTP 400 with the error.

Comparing the redirect_uri strings:

http%3A%2F%2Fwww.noverse.com%2FOAuthStackExchangeCallback http%3A%2F%2Fwww.noverse.com%2FOAuthStackExchangeCallback

They match.

Supporting Data

• Using the GTMOauth2 library by Google
• Application ID is 218
• Client Side OAuth is turned off (so I do see the redirect in the browser)
• The domain name is noverse.com

Code

The code is from the example in the library

The Authenticator Object

This is the object that is used to get the token and to make further secured requests

- (GTMOAuth2Authentication *)authForStackExchange
{
    NSURL *tokenURL = [NSURL URLWithString:@"https://stackexchange.com/oauth/access_token"];
    NSString *redirectURI = @"http://www.noverse.com/OAuthStackExchangeCallback";

    // ... snip ...

    GTMOAuth2Authentication *auth;
    auth = [GTMOAuth2Authentication authenticationWithServiceProvider:@"StackExchange" tokenURL:tokenURL redirectURI:redirectURI clientID:clientID clientSecret:clientSecret];
    return auth;
}

Login to StackExchange

This code starts the process by launching a web browser to enable login and authorization. It intercepts the redirect_uri and then uses the previous object to request the token.

- (void)signInToStackExchange 
{    
    GTMOAuth2Authentication *auth = [self authForStackExchange];
    auth.scope = @"";

    // display the authentication sheet
    NSURL *authURL = [NSURL URLWithString:@"https://stackexchange.com/oauth"];

    GTMOAuth2WindowController *windowController;
    windowController = [GTMOAuth2WindowController controllerWithAuthentication:auth authorizationURL:authURL keychainItemName:kStackExchangeKeychainItemName resourceBundle:nil];

    [windowController signInSheetModalForWindow:self.window delegate:self finishedSelector:@selector(windowController:finishedWithAuth:error:)];
}