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# Fluent API (JwtBuilder)

`jwtNew()` returns a `JwtBuilder` object that lets you compose a JWT one method at a time. Every claim/header method returns `this` so calls can be chained. Terminate the chain with `.sign()` (JWS) or `.encrypt()` (JWE) to produce the compact token string.

## Claim Methods

| Method                | Signature                | Description                                                      |
| --------------------- | ------------------------ | ---------------------------------------------------------------- |
| `subject( val )`      | `(any) → this`           | Sets the `sub` claim.                                            |
| `issuer( val )`       | `(any) → this`           | Sets the `iss` claim.                                            |
| `audience( val )`     | `(string\|array) → this` | Sets the `aud` claim. Accepts a string or an array of audiences. |
| `claim( key, val )`   | `(string, any) → this`   | Sets an arbitrary custom claim.                                  |
| `withPayload( val )`  | `(struct) → this`        | Replaces the entire payload with the given struct.               |
| `expireIn( seconds )` | `(numeric) → this`       | Sets `exp` as `now() + seconds`.                                 |
| `expireAt( date )`    | `(date) → this`          | Sets `exp` to an explicit DateTime.                              |
| `issuedNow()`         | `() → this`              | Sets `iat` to `now()`.                                           |
| `issuedAt( date )`    | `(date) → this`          | Sets `iat` to an explicit DateTime.                              |
| `notBefore( date )`   | `(date) → this`          | Sets the `nbf` claim.                                            |
| `jti( val )`          | `(any) → this`           | Sets the `jti` (JWT ID) claim.                                   |

## Header Methods

| Method               | Signature              | Description                                          |
| -------------------- | ---------------------- | ---------------------------------------------------- |
| `header( key, val )` | `(string, any) → this` | Sets a JOSE header field (e.g. `kid`, `typ`, `cty`). |

## Terminal Methods

| Method                                             | Signature                           | Returns  | Description                                  |
| -------------------------------------------------- | ----------------------------------- | -------- | -------------------------------------------- |
| `sign( [key], [algorithm] )`                       | `(any?, string?) → string`          | `string` | Signs and returns the compact JWS string.    |
| `encrypt( [key], [keyAlgorithm], [encAlgorithm] )` | `(any?, string?, string?) → string` | `string` | Encrypts and returns the compact JWE string. |

When the terminal arguments are omitted, the builder falls back to the module's `defaultSigningKey` / `defaultAlgorithm` (or `defaultEncryptionKey` / `defaultKeyAlgorithm` / `defaultEncAlgorithm` for `.encrypt()`).

## Examples

```javascript
// HMAC with custom headers
token = jwtNew()
    .subject( "alice" )
    .claim( "tenant", "acme-corp" )
    .expireIn( 900 )
    .header( "kid", "signing-key-v2" )
    .sign( secret, "HS256" );

// RSA with all standard claims
token = jwtNew()
    .subject( "svc-account" )
    .issuer( "auth-service" )
    .audience( [ "api", "analytics" ] )
    .issuedNow()
    .expireIn( 3600 )
    .jti( createUUID() )
    .sign( privateKeyPem, "RS256" );

// JWE encryption
token = jwtNew()
    .subject( "patient-456" )
    .claim( "phi", { dob: "1990-01-15", ssn: "xxx-xx-1234" } )
    .encrypt( secret, "dir", "A256GCM" );

// Re-use an existing payload struct
payload = { sub: "user-1", iss: "my-api", roles: [ "admin" ] };
token   = jwtNew().withPayload( payload ).expireIn( 3600 ).sign( secret, "HS256" );
```

## Related

* [JWTNew()](/boxlang-framework/modularity/jwt/reference/built-in-functions/jwtnew.md) — the BIF that returns the builder
* [Fluent Builder Guide](/boxlang-framework/modularity/jwt/fluent-builder.md)
* [JWTCreate()](/boxlang-framework/modularity/jwt/reference/built-in-functions/jwtcreate.md) — functional equivalent
* [JWTEncrypt()](/boxlang-framework/modularity/jwt/reference/built-in-functions/jwtencrypt.md) — functional equivalent for JWE


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