Background

As ManagedIdentityCredential's API surfaced has evolved, the following 2 ctors are no longer recommended:

From a behavioral perspective, the following ctors are equivalent:

ManagedIdentityCredential credential1 = new();
ManagedIdentityCredential credential2 = new(ManagedIdentityId.SystemAssigned);

ManagedIdentityCredential credential1 = new("<client_id>");
ManagedIdentityCredential credential2 = new(ManagedIdentityId.FromUserAssignedClientId("<client-id>"));

The same is true for the following 2 ctors:

ManagedIdentityCredential credential1 = new(new ResourceIdentifier("<resource_id>"));
ManagedIdentityCredential credential2 = new(
    ManagedIdentityId.FromUserAssignedResourceId(new ResourceIdentifier("<resource_id>")));

The newer ctors make the intent clear; that is, whether system-assigned or user-assigned managed identity is to be used. Furthermore, the older ctors are already suppressed from display in IntelliSense and Learn API ref docs (thanks to [EditorBrowsable(EditorBrowsableState.Never)].

Proposal

Discourage further use of the 2 older ctors by deprecating them. To accomplish this, apply the following [Obsolete()] attribute to each of them:

[Obsolete("Use constructor ManagedIdentityCredential(ManagedIdentityId id, TokenCredentialOptions options = null) or ManagedIdentityCredential(ManagedIdentityCredentialOptions options).")]

The result is fewer ways to accomplish the same thing and a much clearer intent.

Finally, add a CHANGELOG entry to raise awareness of the deprecated ctors.