Fixed client_secret missing if client_id is provided as body param

[nilswieber]

Sometimes OAuthClients do a TokenRequest with the client_id in the body (without the client_secret) and provide client_id and client_secret in the authorization header.

So the clientId would be !=null but the clientSecret == null.
In that case the authorization header won't be evaluated.

This pull request fixes this issue.

[rossitsaborissova]

Please, add a unit test for that case. Also, please add the issue number in your commit messages, i.e. "[Issue #92] Fixed client_secret missing if client_id is provided as body param" for the current issue. Thanks!

[rossitsaborissova]

Please, see my previous comment.
Thanks for your interest in the project.

[rossitsaborissova]

I logged an issue for that problem and send a pull request - #95. The connectTimeout and mongo-java-driver issues will be logged as separate tasks.