feat: add authority param support to DSN (#546)

Signed-off-by: Marco Pracucci <marco@pracucci.com>

Author: pracucci

connection_properties.go

@@ -286,6 +286,17 @@ var propertyEndpoint = createConnectionProperty(
 	connectionstate.ContextStartup,
 	connectionstate.ConvertString,
 )
+var propertyAuthority = createConnectionProperty(
+	"authority",
+	"The expected server name in the TLS handshake. By default, the endpoint hostname is used. This option "+
+		"is useful when connecting to Spanner via Google Private Connect or other custom endpoints where the "+
+		"endpoint hostname does not match the server’s TLS certificate.",
+	"",
+	false,
+	nil,
+	connectionstate.ContextStartup,
+	connectionstate.ConvertString,
+)
 var propertyCredentials = createConnectionProperty(
 	"credentials",
 	"The location of the credentials file to use for this connection. If neither this property or encoded "+

driver.go

@@ -372,6 +372,10 @@ type ConnectorConfig struct {
 	// Leave this empty to use the standard Spanner API endpoint.
 	Host string
 
+	// The expected server name in the TLS handshake.
+	// Leave this empty to use the endpoint hostname.
+	Authority string
+
 	// Project, Instance, and Database identify the database that the connector
 	// should create connections for.
 	Project  string
@@ -568,6 +572,10 @@ func createConnector(d *Driver, connectorConfig ConnectorConfig) (*connector, er
 	if connectorConfig.Host != "" {
 		opts = append(opts, option.WithEndpoint(connectorConfig.Host))
 	}
+	assignPropertyValueIfExists(state, propertyAuthority, &connectorConfig.Authority)
+	if connectorConfig.Authority != "" {
+		opts = append(opts, option.WithGRPCDialOption(grpc.WithAuthority(connectorConfig.Authority)))
+	}
 	if val := propertyCredentials.GetValueOrDefault(state); val != "" {
 		opts = append(opts, option.WithCredentialsFile(val))
 	}