[wip] switch to oauthlib from python-oauth2

lower-level implementation, but more robust and gives us more control

jupyterhub/orm.py

@@ -513,6 +513,7 @@ class OAuthCode(Base):
     expires_at = Column(Integer)
     redirect_uri = Column(Unicode(1023))
     session_id = Column(Unicode(255))
+    # state = Column(Unicode(1023))
     user_id = Column(Integer, ForeignKey('users.id', ondelete='CASCADE'))
 
 
@@ -524,6 +525,10 @@ class OAuthClient(Base):
     secret = Column(Unicode(255))
     redirect_uri = Column(Unicode(1023))
 
+    @property
+    def client_id(self):
+        return self.identifier
+
     access_tokens = relationship(
         OAuthAccessToken,
         backref='client',