I am attempting to use the /me API to retrieve an authenticated user's details but I am receiving a 400 error.

I am able to complete the OAuth2 dance and have been able to capture the access token and expire value, but when I then go on to send my request to https://api.stackexchange.com/2.0/me?site=stackoverflow (including access token) it gives me a 400 error.

Here is what I am logging if it's of any use:

GET request for "https://api.stackexchange.com/2.0/me?site=stackoverflow" resulted in 400 (Bad Request); invoking error handler
HttpClientErrorException while completing connection: 400 Bad Request
Response body: ?

Is there anything I am missing? other than just sending the access token to the above URL is there anything else I need to do?