[Feature Request] Add support for Managed Identity

[bgavrilMS]

Support in MSAL .NET - https://learn.microsoft.com/en-us/entra/msal/dotnet/advanced/managed-identity

More in-depth technical spec here. DotNet implementation here. All MSALs support it (Java, Py, NodeJS).

• Get the PR / CI builds working again (most likely need to move them from GitHub to ADO)
• Public API support (new client, ways to specify between UAMI and SAMI, disable token cache serialization extensibilty)
• Detect MSI source + public API for Azure SDK for this (probing API ... see .NET too)
• Code up the 5 MSI sources (check Azure SDK's implementation, should be mostly copy-paste)
• Error handling code
• AcquireTokenForManagedIdentity should throw if a user-assigned managed identity clientID or resourceID is supplied when not supported microsoft-authentication-library-for-dotnet#4837
• Manual testing of each MSI source (this is the most consuming task). Do negative testing as well to check error handling.
• Static caching of all MSI tokens (including adding a property TokenSource on the AutheticationResult)
• Retry policy for MSI (create public API to disable retry policies, abstract retry policy in MSAL, add linear retry 3 times with 1s interval to MSI)
• Update Sample with MSAL Go implementation - https://learn.microsoft.com/en-us/entra/msal/dotnet/advanced/managed-identity
• Update docs
• Review support for FIC, update samples etc.

[bgavrilMS]

For the retry policy I recommend you see the 3 PRs in MSAL Node:

AzureAD/microsoft-authentication-library-for-js#6891
AzureAD/microsoft-authentication-library-for-js#6950
AzureAD/microsoft-authentication-library-for-js#6920