New AWS Okta SSO authentication approach

[maxtacu]

Token retrieval fails
Only if your organization switches to the new SSO auth approach described here
https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-sso.html
and here https://www.okta.com/blog/2020/05/how-okta-aws-sso-simplifies-admin-and-adds-cli-support/
then you might face issues described below

To Reproduce
Steps to reproduce the behavior:

1. Configure a working ~/.okta-aws file with profiles
2. okta-awscli -s and select any profile
3. Enter credentials for login
4. See error smth like this:

ERROR - No Extra Verification
Traceback (most recent call last):
  File "/Users/mtacu/.pyenv/versions/3.8.13/bin/okta-awscli", line 33, in <module>
    sys.exit(load_entry_point('okta-awscli', 'console_scripts', 'okta-awscli')())
  File "/Users/mtacu/.pyenv/versions/3.8.13/lib/python3.8/site-packages/click/core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "/Users/mtacu/.pyenv/versions/3.8.13/lib/python3.8/site-packages/click/core.py", line 1055, in main
    rv = self.invoke(ctx)
  File "/Users/mtacu/.pyenv/versions/3.8.13/lib/python3.8/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/mtacu/.pyenv/versions/3.8.13/lib/python3.8/site-packages/click/core.py", line 760, in invoke
    return __callback(*args, **kwargs)
  File "/Users/mtacu/maxdoesdevops/okta-awscli/oktaawscli/okta_awscli.py", line 141, in main
    get_credentials(
  File "/Users/mtacu/maxdoesdevops/okta-awscli/oktaawscli/okta_awscli.py", line 36, in get_credentials
    _, assertion = okta.get_assertion()
  File "/Users/mtacu/maxdoesdevops/okta-awscli/oktaawscli/okta_auth.py", line 165, in get_assertion
    assertion = self.get_saml_assertion(resp)
  File "/Users/mtacu/maxdoesdevops/okta-awscli/oktaawscli/okta_auth.py", line 149, in get_saml_assertion
    self.logger.error("SAML assertion not valid: " + assertion)
TypeError: can only concatenate str (not "NoneType") to str

Environment (please complete the following information):

• Any OS environment because the error comes from Okta due to changed auth approach

Additional context
Issue is created to track development progress and inform other users of a known issue. Further updates about this issue will be posted here

[TryTryAgain]

Same, it does appear to work when MFA is disabled but that's not gonna work for us.