libcmis: Google Drive login no longer working

Hi all,

investigating the cause of tdf#98416 [1] I came across a problem in libcmis.

The problem depends on the Google change of the page sequence in its 
general login.

A somewhat deeper description.

In libcmis Google OAuth 2.0 is coded in OAuth2Providers::OAuth2Gdrive.

In that member function the interaction with Google is carried out by 
parsing the received html pages and then post the required fields.

From the first activating URL and libcmis code I believe 'Google OAuth 
2.0 for Web Server Applications' HTTP/REST interaction mode is implemented.

Unfortunately Google changed the login sequence [2] from a single page 
scheme (user email + password) to a two pages scheme, first page to 
input the user email, the second page to input user password.

That broke libcmis Google driver login.

I figured out a fix, for the time being as a patch in external/libcmis.

In Linux it works, I'll test it on Windows before submitting to Gerrit.

--
Kind Regards,
Giuseppe Castagno aka beppec56
Acca Esse http://www.acca-esse.eu
giuseppe.castagno at acca-esse.eu

[1] https://bugs.documentfoundation.org/show_bug.cgi?id=98416
[2] https://productforums.google.com/forum/#!topic/gmail/oAsE-6wmaSU