fix: better support for fallback mode

protos/google/cloud/bigquery/connection/v1/connection.proto

@@ -233,6 +233,9 @@ message Connection {
     // Amazon Web Services (AWS) properties.
     AwsProperties aws = 8;
 
+    // Azure properties.
+    AzureProperties azure = 11;
+
     // Cloud Spanner properties.
     CloudSpannerProperties cloud_spanner = 21;
 
@@ -275,6 +278,13 @@ message CloudSqlProperties {
 
   // Input only. Cloud SQL credential.
   CloudSqlCredential credential = 4 [(google.api.field_behavior) = INPUT_ONLY];
+
+  // Output only. The account ID of the service used for the purpose of this connection.
+  //
+  // When the connection is used in the context of an operation in
+  // BigQuery, this service account will serve as identity being used for
+  // connecting to the CloudSQL instance specified in this connection.
+  string service_account_id = 5 [(google.api.field_behavior) = OUTPUT_ONLY];
 }
 
 // Credential info for the Cloud SQL.
@@ -301,7 +311,8 @@ message AwsProperties {
   oneof authentication_method {
     // Authentication using Google owned AWS IAM user's access key to assume
     // into customer's AWS IAM Role.
-    AwsCrossAccountRole cross_account_role = 2;
+    // Deprecated, do not use.
+    AwsCrossAccountRole cross_account_role = 2 [deprecated = true];
 
     // Authentication using Google owned service account to assume into
     // customer's AWS IAM Role.
@@ -337,6 +348,34 @@ message AwsAccessRole {
   string identity = 2;
 }
 
+// Container for connection properties specific to Azure.
+message AzureProperties {
+  // Output only. The name of the Azure Active Directory Application.
+  string application = 1 [(google.api.field_behavior) = OUTPUT_ONLY];
+
+  // Output only. The client id of the Azure Active Directory Application.
+  string client_id = 2 [(google.api.field_behavior) = OUTPUT_ONLY];
+
+  // Output only. The object id of the Azure Active Directory Application.
+  string object_id = 3 [(google.api.field_behavior) = OUTPUT_ONLY];
+
+  // The id of customer's directory that host the data.
+  string customer_tenant_id = 4;
+
+  // The URL user will be redirected to after granting consent during connection
+  // setup.
+  string redirect_uri = 5;
+
+  // The client id of the user's Azure Active Directory Application used for a
+  // federated connection.
+  string federated_application_client_id = 6;
+
+  // Output only. A unique Google-owned and Google-generated identity for the Connection.
+  // This identity will be used to access the user's Azure Active Directory
+  // Application.
+  string identity = 7 [(google.api.field_behavior) = OUTPUT_ONLY];
+}
+
 // Container for connection properties for delegation of access to GCP
 // resources.
 message CloudResourceProperties {