Is your feature request related to a problem? Please describe.
I have set up OAuth2 and am able to receive valid access token for cloud spanner. However, I'm unable to use it to form a proper Connection object using the jdbc driver. The JdbcDriver.connect() method only accepts url for a credentials file.

Describe the solution you'd like
I'd like for JdbcDriver.connect(String url, Properties info) to accept oauth token in its Properties parameter.

Describe alternatives you've considered
by not specifying any credentials, the default credentials of the environment as returned by GoogleCredentials.getApplicationDefault() will be used. However, this also requires a json file, and does not use an access token.

Additional Notes
this is the same request as olavloite/spanner-jdbc#6