BasicAuthProvider should check the method is Basic

[cemcatik]

I ran across this issue when I send requests where the Authorization header was a JWT Bearer such as:

Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.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.mWXfWsFomqMnMBHgZUoHNTONmAbrKoUIpG5stzrjNHo

When the BasicAuthProvider tries to parse the credentials it Base64 decodes "Bearer eyJ0eXAiOiJKV1Q..." and since the resulting string has a : in it thinks it's a Basic Auth header. This PR makes sure the header is Basic Auth and returns None otherwise.

[akkie]

Thanks!

[cemcatik]

Any time