Merge pull request #528 from AzureAD/SJAIN/Documentation-update

Documentation update for App token provider

Author: siddhijain

src/main/java/com/microsoft/aad/msal4j/ClientCredentialRequest.java

@@ -11,6 +11,9 @@
 class ClientCredentialRequest extends MsalRequest {
 
     ClientCredentialParameters parameters;
+    /** AppTokenProvider creates a Credential from a function that provides access tokens. The function
+       must be concurrency safe. This is intended only to allow the Azure SDK to cache MSI tokens. It isn't
+     useful to applications in general because the token provider must implement all authentication logic. */
     Function<AppTokenProviderParameters, CompletableFuture<TokenProviderResult>> appTokenProvider;
 
     ClientCredentialRequest(ClientCredentialParameters parameters,

src/main/java/com/microsoft/aad/msal4j/ConfidentialClientApplication.java

@@ -34,6 +34,9 @@ public class ConfidentialClientApplication extends AbstractClientApplicationBase
     private boolean clientCertAuthentication = false;
     private ClientCertificate clientCertificate;
 
+    /** AppTokenProvider creates a Credential from a function that provides access tokens. The function
+     must be concurrency safe. This is intended only to allow the Azure SDK to cache MSI tokens. It isn't
+     useful to applications in general because the token provider must implement all authentication logic. */
     public Function<AppTokenProviderParameters, CompletableFuture<TokenProviderResult>> appTokenProvider;
 
     @Accessors(fluent = true)