public override async Task <SignatureVerificationFailure> Verify(HttpRequestForSigning signedRequest, Signature signature, Client client) { if (string.IsNullOrEmpty(signature.Nonce)) { return(null); } var previousNonce = await _nonceStore.Get(client.Id, signature.Nonce).ConfigureAwait(false); if (previousNonce != null && previousNonce.Expiration >= _systemClock.UtcNow) { return(SignatureVerificationFailure.ReplayedRequest($"The nonce '{previousNonce.Value}' for client {client.Id} ({client.Name}) is not unique and has been used before. It expires at {previousNonce.Expiration:R}.")); } var nonce = new Nonce( clientId: client.Id, value: signature.Nonce, expiration: _systemClock.UtcNow.Add(client.NonceLifetime)); await _nonceStore.Register(nonce).ConfigureAwait(false); return(null); }