port: Managed Identity (MSI) + Single Tenant support for Bot apps (#5829)

[github-actions]

The changes in Managed Identity (MSI) + Single Tenant support for Bot apps (#5829) may need to be ported to maintain parity with microsoft/botbuilder-dotnet.

Fixes #5830

Description

• Enable Azure's Managed Identity (MSI) for bot apps, so that bot authors don't have to manage app secrets.
• Support for hosting bots as single tenant apps, which enables acquiring AAD access tokens from the bot's host tenant, as opposed to, botframework.com tenant.

Below are the 3 ways a bot app can now be hosted:

1. Multi-Tenant (Default):

{
  "MicrosoftAppId": "",
  "MicrosoftAppPassword": ""
}

2. Single Tenant:

{
  "MicrosoftAppType": "SingleTenant",
  "MicrosoftAppId": "",
  "MicrosoftAppPassword": "",
  "MicrosoftAppTenantId": ""
}

3. Managed Identity (MSI):

{
  "MicrosoftAppType": "UserAssignedMSI",
  "MicrosoftAppId": "",
  "MicrosoftAppTenantId": ""
}

Specific Changes

• Added classes for Managed Identity credentials management and token acquisition.
• Updated ConfigurationServiceClientCredentialFactory to instantiate the appropriate credential mechanism (MultiTenant/SingleTenant/MSI) based on appsettings.
• Added the bot's host tenant as a valid JWT token issuer since the tokens will be issued from the host tenant when using SingleTenant/MSI hosting model. This was done by adding a property to the AuthenticationConfiguration class which would be used in the skills scenarios.
• Added an overload in PasswordServiceClientCredentialsFactory to accept TenantId which can be used to acquire token using the bot's host tenant for SingleTenant scenario.

Testing

Following scenarios were verified:

1. Bot to Channel scenarios:

• MultiTenant
• SingleTenant
• MSI

2. Bot to bot (skills) scenarios:

	MultiTenant Skill	SingleTenant Skill	MSI Skill
MultiTenant Host	Y	-	-
SingleTenant Host	-	Y	Y
MSI Host	-	Y	Y

NOTE: When one of the bots is MultiTenant, the other cannot be SingleTenant/MSI since the token acquisition by the MultiTenant bot will fail due to not being able to find the SingleTenant/MSI bot resource registered in the `botframework.com` tenant. So, those scenarios are not supported.

Please review and, if necessary, port the changes.

[stevengum]

Note that for the SingleTenant Skill-MSI Skill scenarios to work, the bots must be in the same tenant.