With alpha2 without using the constraints https://github.com/apache/airflow/blob/constraints-master/constraints-3.6.txt , when accessing Webserver it fails with

```
Something bad has happened.
Please consider letting us know by creating a bug report using GitHub.

Python version: 3.6.12
Airflow version: 2.0.0a2
Node: 599861bd62ac
-------------------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 2447, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1953, in full_dispatch_request
    return self.finalize_request(rv)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1970, in finalize_request
    response = self.process_response(response)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 2269, in process_response
    self.session_interface.save_session(self, ctx.session, response)
  File "/usr/local/lib/python3.6/site-packages/flask/sessions.py", line 387, in save_session
    samesite=samesite,
  File "/usr/local/lib/python3.6/site-packages/werkzeug/wrappers/base_response.py", line 479, in set_cookie
    samesite=samesite,
  File "/usr/local/lib/python3.6/site-packages/werkzeug/http.py", line 1217, in dump_cookie
    raise ValueError("SameSite must be 'Strict', 'Lax', or 'None'.")
ValueError: SameSite must be 'Strict', 'Lax', or 'None'.
```
setup.py
'github_enterprise': flask_oauth,
    'google': google,
    'google_auth': flask_oauth,
    'grpc': grpc,
    'hashicorp': hashicorp,
    'hdfs': hdfs,  
    'hive': hive,  
    'jdbc': jdbc,
    'jira': jira,
    'kerberos': kerberos,
    'kubernetes': kubernetes,   
    'ldap': ldap,
    "microsoft.azure": azure,
    "microsoft.mssql": mssql,
    "microsoft.winrm": winrm,
    'mongo': mongo,
    'mssql': mssql,  
    'mysql': mysql,
    'odbc': odbc,
    'oracle': oracle,
    'pagerduty': pagerduty,
    'papermill': papermill,
    'password': password,
    'pinot': pinot,  
    'plexus': plexus,
    'postgres': postgres,
    'presto': presto,
    'qds': qds,
    'rabbitmq': rabbitmq,
    'redis': redis,