Adding a method for exchanging 2FA token to the SAML response

[yevgenkre]

The Epic integration uses the SAML response from the Duo server to handle the authentication on it's end. This change introduces the method to retrieve the SAML response in the end of the authentication in exchange to the 2FA token.

Description

Added a method ExchangeAuthorizationCodeForSamlResponse(string duoCode, string username) which sends the 2FA token to the Duo server, receives the response and returns the samlResponse part of it.

Motivation and Context

This change is a part of the bigger effort of migrating Epic integration to the Universal Prompt from the legacy implementation. For this reason the Universal Prompt needs to support the SAML response.

How Has This Been Tested?

Added unit tests, specific for SAML response. Made sure that the existing unit tests pass

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)