Incorrectly formatted access tokens may cause a FormatException

[Archomeda]

Whenever the access token is invalid according to (some) specifications, performing a request can throw a FormatException. An example is including a single " character.

Failing early is the best solution, so the consumer immediately knows that there's something wrong, instead of finding that out upon the request.
In this case, a pre-validation check in Connection object on the AccessToken property can be added. It will have to check if the token is properly formatted (e.g. does not contain invalid characters).