Support credential JSON for Spanner

Closes authzed#1941

Signed-off-by: Lex Cao <[email protected]>

internal/datastore/spanner/options.go

@@ -14,6 +14,7 @@ type spannerOptions struct {
 	followerReadDelay           time.Duration
 	maxRevisionStalenessPercent float64
 	credentialsFilePath         string
+	credentialsJSON             []byte
 	emulatorHost                string
 	disableStats                bool
 	readMaxOpen                 int
@@ -141,6 +142,14 @@ func CredentialsFile(path string) Option {
 	}
 }
 
+// CredentialsJSON is the json containing credentials for a service
+// account that can access the cloud spanner instance
+func CredentialsJSON(json []byte) Option {
+	return func(so *spannerOptions) {
+		so.credentialsJSON = json
+	}
+}
+
 // EmulatorHost is the URI of a Spanner emulator to connect to for
 // development and testing use
 func EmulatorHost(uri string) Option {

internal/datastore/spanner/spanner.go

@@ -144,6 +144,7 @@ func NewSpannerDatastore(ctx context.Context, database string, opts ...Option) (
 	client, err := spanner.NewClientWithConfig(context.Background(), database,
 		spanner.ClientConfig{SessionPoolConfig: cfg},
 		option.WithCredentialsFile(config.credentialsFilePath),
+		option.WithCredentialsJSON(config.credentialsJSON),
 		option.WithGRPCConnectionPool(max(config.readMaxOpen, config.writeMaxOpen)),
 		option.WithGRPCDialOption(
 			grpc.WithStatsHandler(otelgrpc.NewClientHandler()),