charge-relay

Charge Relay

A one-command Go API and client that accept pathUSD on Tempo Moderato through Tempo API's MPP relay. It mirrors the MPPX relay example: the server issues a pull-mode charge for /api/photo, the client signs it, and the relay validates and broadcasts the credential.

Setup

Create a Tempo API key with the mpp:write scope and provide it only to the server process:

export TEMPO_API_KEY=tempo:sk:...
export TEMPO_API_URL=https://api.tempo.xyz
export MPP_SECRET_KEY=$(openssl rand -base64 32)
go run ./examples/charge-relay

TEMPO_API_URL can target a compatible self-hosted or preview Tempo API. MPP_SECRET_KEY protects the server-issued challenges; the example has a development-only default. The example creates fresh payer and recipient accounts, funds the payer through the Moderato faucet, starts an in-process HTTP server, validates a credential without broadcasting, submits that same credential to /api/photo, and prints the relay receipt reference.

Routes

Route	Description
/api/photo	Payment-gated image URL
/api/health	Free health check

Relay configuration

method, err := charge.MethodFromConfig(charge.Config{
	ChainID:   tempotx.ChainIdModerato,
	Currency:  tempo.DefaultCurrencyForChain(tempotx.ChainIdModerato),
	Recipient: recipient,
	Relay: &charge.RelayConfig{
		APIKey:     os.Getenv("TEMPO_API_KEY"),
		APIBaseURL: os.Getenv("TEMPO_API_URL"),
	},
	SupportedModes: []tempo.ChargeMode{tempo.ChargeModePull},
})

The relay registers separate validation and broadcast hooks through server.IntentHooks. payment.ValidateCredential calls only the relay validation endpoint, while payment.BroadcastCredential re-validates and then calls the broadcast endpoint. Paid HTTP routes use that same split lifecycle automatically. payment.VerifyCredential remains a backwards-compatible alias for the mutating broadcast path.

The relay broadcasts pull credentials and recognizes push credentials as already broadcast transactions, returning their receipts without sending them again. Relay failures expose only safe machine-readable codes.