Add a new RPC ConnectWithCreds to allow gofer to connect to a unix domain socket with application's credentials

pkg/sentry/kernel/auth/context.go

@@ -39,6 +39,14 @@ func CredentialsFromContext(ctx context.Context) *Credentials {
 	return NewAnonymousCredentials()
 }
 
+// CredentialsFromContextOrNil returns a copy of the Credentials used by ctx, or nil if ctx does not have Credentials.
+func CredentialsFromContextOrNil(ctx context.Context) *Credentials {
+	if v := ctx.Value(CtxCredentials); v != nil {
+		return v.(*Credentials)
+	}
+	return nil
+}
+
 // ThreadGroupIDFromContext returns the current thread group ID when ctx
 // represents a task context.
 func ThreadGroupIDFromContext(ctx context.Context) (tgid int32, ok bool) {