Use RequestSecurityCode prompt function to ask for MFA in Okta provider

[FaHeymann]

https://github.com/Versent/saml2aws/pull/744 introduced pinentry as an alternative prompter to allow the user to enter a TOTP token while using saml2aws as the credential_process. To make this work in combination with the Okta provider I would like to change the prompt for MFA in there to also use the RequestSecurityCode prompt function.

[christianmeyer]

duplicate of #790

[FaHeymann]

It's a similar change but in a different provider

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (0ccc00a) 39.72% compared to head (7596b48) 39.72%.

Files	Patch %	Lines
pkg/provider/okta/okta.go	0.00%	1 Missing :warning:

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #796   +/-   ##
=======================================
  Coverage   39.72%   39.72%           
=======================================
  Files          53       53           
  Lines        8027     8027           
=======================================
  Hits         3189     3189           
  Misses       4411     4411           
  Partials      427      427           

Flag	Coverage Δ
unittests	39.72% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.