feat(NODE-7047): use custom credential provider first

Author: durran

src/cmap/auth/mongodb_aws.ts

@@ -63,7 +63,8 @@ export class MongoDBAWS extends AuthProvider {
       );
     }
 
-    if (!authContext.credentials.username) {
+    // If a custom credential provider is present we will use that first.
+    if (this.credentialProvider || !authContext.credentials.username) {
       authContext.credentials = await makeTempCredentials(
         authContext.credentials,
         this.credentialFetcher

test/integration/auth/mongodb_aws.test.ts

@@ -144,12 +144,6 @@ describe('MONGODB-AWS', function () {
         this.skipReason = 'only relevant to AssumeRoleWithWebIdentity with SDK installed';
         return this.skip();
       }
-      // If we have a username the credentials have been set from the URI, options, or environment
-      // variables per the auth spec stated order.
-      if (client.options.credentials.username) {
-        this.skipReason = 'Credentials in the URI on env variables will not use custom provider.';
-        return this.skip();
-      }
     });
 
     it('authenticates with a user provided credentials provider', async function () {