Support for OAuth2

[Louson]

Hello, here is a suggestion for the OAuth2 support. There is an intermediate commit to add the API userinfo as this is the example given by

Related to issue #89

It might not exactly sure it does fit to your coding style, but maybe you can help on this ?

I am not sure neither how this can be automatically tested. Here is a script I have made for tests: https://privatebin.net/?c2c1cd266e29aff2#22qmxEqCGs3Wi9fbbLW61NxxKsYeCSsb2zbs3pNo7bn3

Thanks,