Adopt TokenCredential from @azure/core-auth instead of custom TokenProvider interface

[daviburg]

Context

The Node SDK uses a custom TokenProvider interface that returns Promise<string> (raw token value). The .NET SDK accepts TokenCredential from Azure.Core, which is the standard interface shared by every @azure/* client library.

Parity gap

// Current Node SDK
export interface TokenProvider {
    getAccessTokenAsync(scopes: string[]): Promise<string>;
}

// .NET SDK equivalent (Azure.Core)
public abstract TokenCredential // getToken(TokenRequestContext, CancellationToken): AccessToken

The practical impact:

• Callers using @azure/identity credentials (DefaultAzureCredential, WorkloadIdentityCredential, etc.) must wrap them in ManagedIdentityTokenProvider — an unnecessary adapter
• The SDK cannot be composed with @azure/core-auth credential chains (ChainedTokenCredential, custom TokenCredential implementations)
• No access to token expiry (expiresOnTimestamp) so proactive refresh isn't possible

Proposed change

Replace TokenProvider with TokenCredential from @azure/core-auth:

import { TokenCredential } from "@azure/core-auth";

// ConnectorClientBase constructor becomes:
constructor(connectionRuntimeUrl: string, credential: TokenCredential, options?: ConnectorClientOptions)

@azure/core-auth is already a transitive dependency (via @azure/identity). Promoting it to a direct peer dependency and using TokenCredential directly aligns the Node SDK with every other @azure/* package.

This is a breaking API change — best paired with the @azure/core-rest-pipeline adoption (where BearerTokenCredentialPolicy consumes TokenCredential directly).

Azure SDK guideline

• DO use TokenCredential from @azure/core-auth