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# Server \[Protect endpoints with payment requirements]

Create a payment handler with `server.New()` and use `ChargeMiddleware` or call `Charge()` directly. The `charge.NewMethod` factory configures `Currency` and `Recipient` once, then every charge uses those defaults.

## Quick start

```go [server.go]
import (
	"github.com/tempoxyz/mpp-go/pkg/server"
	charge "github.com/tempoxyz/mpp-go/pkg/tempo/server"
)

intent, _ := charge.NewIntent(charge.IntentConfig{
	RPCURL: "https://rpc.tempo.xyz",
})
method := charge.NewMethod(charge.MethodConfig{
	Intent:    intent,
	Recipient: "0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266",
})
payment := server.New(method, "api.example.com", "my-server-secret")

result, err := payment.Charge(ctx, server.ChargeParams{
	Authorization: r.Header.Get("Authorization"),
	Amount:        "0.50",
})

if result.IsChallenge() {
	server.WriteChallenge(w, result.Challenge, payment.Realm())
	return
}
// result.Receipt is the verified Receipt
```

## Framework middleware

### net/http

Use `server.ChargeMiddleware` to wrap any `http.Handler`:

```go
mux := http.NewServeMux()
mux.Handle("/resource", server.ChargeMiddleware(payment, server.ChargeParams{
	Amount:      "0.50",
	Description: "Paid resource",
})(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	credential := server.CredentialFromContext(r.Context())
	json.NewEncoder(w).Encode(map[string]any{
		"data":  "paid content",
		"payer": credential.Source,
	})
})))
```

### Gin

Use `ginadapter.ChargeMiddleware` from `pkg/server/gin`:

```go
import ginadapter "github.com/tempoxyz/mpp-go/pkg/server/gin"

r := gin.Default()
r.GET("/resource", ginadapter.ChargeMiddleware(payment, server.ChargeParams{
	Amount: "0.50",
}), func(c *gin.Context) {
	credential := server.CredentialFromContext(c.Request.Context())
	c.JSON(200, gin.H{"payer": credential.Source})
})
```

### Echo

Use `echoadapter.ChargeMiddleware` from `pkg/server/echo`:

```go
import echoadapter "github.com/tempoxyz/mpp-go/pkg/server/echo"

e := echo.New()
e.GET("/resource", func(c echo.Context) error {
	credential := server.CredentialFromContext(c.Request().Context())
	return c.JSON(200, map[string]any{"payer": credential.Source})
}, echoadapter.ChargeMiddleware(payment, server.ChargeParams{
	Amount: "0.50",
}))
```

### Chi

Use `server.ChargeMiddleware` with `chi.With`:

```go
r := chi.NewRouter()
r.With(server.ChargeMiddleware(payment, server.ChargeParams{
	Amount: "0.50",
})).Get("/resource", func(w http.ResponseWriter, r *http.Request) {
	credential := server.CredentialFromContext(r.Context())
	json.NewEncoder(w).Encode(map[string]any{"payer": credential.Source})
})
```

## `MethodConfig` parameters

### ChainID (optional)

* **Type:** `int64`

Explicitly bind issued Challenges to a specific chain. If omitted, `mpp-go` infers it from `IntentConfig.RPCURL` when it matches a known Tempo RPC endpoint.

### Currency (optional)

* **Type:** `string`
* **Default:** USDC.e on mainnet, pathUSD on testnet

TIP-20 token address for charges.

### Decimals (optional)

* **Type:** `int`
* **Default:** `6`

Token decimal places for dollar-to-base-unit conversion.

### FeePayer (optional)

* **Type:** `bool`
* **Default:** `false`

Enable fee sponsorship for all Challenges. When enabled, the server co-signs and sponsors transaction gas fees.

### FeePayerURL (optional)

* **Type:** `string`

URL of a remote co-signer when the server does not sign locally.

### Intent

* **Type:** `*charge.Intent`

Intent instance created by `charge.NewIntent`.

### Memo (optional)

* **Type:** `string`

Default memo attached to Challenges.

### Recipient (optional)

* **Type:** `string`

Default recipient address for charges.

### SupportedModes (optional)

* **Type:** `[]tempo.ChargeMode`

Supported Credential submission modes (for example, `pull`, `push`).

## `IntentConfig` parameters

### FeePayerPrivateKey (optional)

* **Type:** `string`

Hex-encoded private key for fee sponsorship. The server co-signs and sponsors transaction gas fees.

### FeePayerSigner (optional)

* **Type:** `*temposigner.Signer`

Custom signer for fee sponsorship. Takes precedence over `FeePayerPrivateKey`.

### RPC (optional)

* **Type:** `tempo.RPCClient`

Custom RPC client instance. Takes precedence over `RPCURL`.

### RPCURL (optional)

* **Type:** `string`
* **Default:** `"https://rpc.tempo.xyz"`

Tempo RPC endpoint URL.

### Store (optional)

* **Type:** `tempo.Store`

Replay-protection store for hash and proof Credentials. Defaults to an in-memory store.

## `ChargeParams` parameters

### Amount

* **Type:** `string`

Payment amount in dollars (for example, `"0.50"` for $0.50). Automatically converted to base units using the configured decimals.

### Authorization (optional)

* **Type:** `string`

The `Authorization` header value from the incoming request.

### ChainID (optional)

* **Type:** `int64`

Override the method's default chain ID for this charge.

### Currency (optional)

* **Type:** `string`

Override the method's default currency address.

### Description (optional)

* **Type:** `string`

Human-readable description attached to the Challenge.

### Expires (optional)

* **Type:** `string`

Challenge expiration as ISO 8601 timestamp. Defaults to 5 minutes from now.

### ExternalID (optional)

* **Type:** `string`

Merchant reference ID for reconciliation.

### FeePayer (optional)

* **Type:** `bool`

Override the method's default fee sponsorship setting for this charge.

### FeePayerURL (optional)

* **Type:** `string`

Override the method's default fee payer URL for this charge.

### Memo (optional)

* **Type:** `string`

Memo attached to this Challenge.

### Meta (optional)

* **Type:** `map[string]string`

Arbitrary metadata attached to the Challenge.

### Recipient (optional)

* **Type:** `string`

Override the method's default recipient address.

### Splits (optional)

* **Type:** `[]tempo.SplitParams`

Split the payment across multiple recipients.

### SupportedModes (optional)

* **Type:** `[]tempo.ChargeMode`

Override supported submission modes for this charge.

## Fee sponsorship

Sponsor gas fees so clients do not need native tokens. Pass `FeePayerPrivateKey` in the `IntentConfig`:

```go
intent, _ := charge.NewIntent(charge.IntentConfig{
	RPCURL:             "https://rpc.tempo.xyz",
	FeePayerPrivateKey: os.Getenv("FEE_PAYER_KEY"),
})
method := charge.NewMethod(charge.MethodConfig{
	Intent:    intent,
	Recipient: "0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266",
})
```

When fee sponsorship is enabled, the server co-signs transactions and covers gas fees on behalf of the client.

## Context helpers

| Function | Description |
|----------|-------------|
| `CredentialFromContext(ctx)` | Extract the verified Credential from request context |
| `ReceiptFromContext(ctx)` | Extract the verified Receipt from request context |
| `ContextWithPayment(ctx, credential, receipt)` | Store payment data in context |

## Key types

| Type | Description |
|------|-------------|
| `ChargeParams` | Parameters for a single charge |
| `IntentConfig` | Configuration for `charge.NewIntent` |
| `MethodConfig` | Configuration for `charge.NewMethod` |
| `Mpp` | Server handler binding method, realm, and secret |
| `ChargeResult` | Charge result containing either a Challenge or a Receipt |
| `SplitParams` | Payment split recipient and amount |