feat(jsonwebtoken): expose decode header utility (#795)

* feat: expose decode header utility

* style: apply linting rules

* fix: minor adjustments & add test suite

* style: apply linting rules in test suite

* fix: algorithm transformation & decode header fn

* style: apply linting rules

* fix: apply clippy suggestions

* fix: simplified decode_header fn & generated index.{js,d.ts}

packages/jsonwebtoken/__tests__/jsonwebtoken.spec.ts

@@ -4,7 +4,7 @@ import { join } from 'node:path'
 import test from 'ava'
 import { decode as nodeJwtDecode } from 'jsonwebtoken'
 
-import { Algorithm, sign, signSync, verifySync, verify } from '../index.js'
+import { Algorithm, sign, signSync, verifySync, verify, decodeHeader } from '../index.js'
 
 const getUtcTimestamp = () => Math.floor(new Date().getTime() / 1000)
 const oneDayInSeconds = 86400
@@ -30,6 +30,20 @@ test('signSync and sign (async) should produce the same result', async (t) => {
   t.truthy(nodeJwtDecode(resAsync))
 })
 
+test('should decode header', async (t) => {
+  const data = {
+    id: 'f81d4fae-7dec-11d0-a765-00a0c91e6bf6',
+  }
+  const claims = { data, exp: getUtcTimestamp() + oneDayInSeconds }
+  const secretKey = 'secret'
+  const headers = { algorithm: Algorithm.HS384 }
+
+  const token = await sign(claims, secretKey, headers)
+
+  const header = decodeHeader(token)
+  t.is(header.algorithm, Algorithm.HS384)
+})
+
 test('verify should return the decoded claims', async (t) => {
   const data = {
     id: 'f81d4fae-7dec-11d0-a765-00a0c91e6bf6',

packages/jsonwebtoken/index.d.ts

@@ -28,6 +28,8 @@ export const enum Algorithm {
   EdDSA = 11
 }
 
+export function decodeHeader(token: string): Header
+
 export interface Header {
   /**
    * The algorithm used

packages/jsonwebtoken/index.js

@@ -347,6 +347,7 @@ if (!nativeBinding) {
 }
 
 module.exports.Algorithm = nativeBinding.Algorithm
+module.exports.decodeHeader = nativeBinding.decodeHeader
 module.exports.sign = nativeBinding.sign
 module.exports.signSync = nativeBinding.signSync
 module.exports.verify = nativeBinding.verify

packages/jsonwebtoken/src/algorithm.rs

@@ -48,6 +48,26 @@ impl From<Algorithm> for jsonwebtoken::Algorithm {
   }
 }
 
+impl From<jsonwebtoken::Algorithm> for Algorithm {
+  #[inline]
+  fn from(value: jsonwebtoken::Algorithm) -> Self {
+    match value {
+      jsonwebtoken::Algorithm::ES256 => Algorithm::ES256,
+      jsonwebtoken::Algorithm::ES384 => Algorithm::ES384,
+      jsonwebtoken::Algorithm::EdDSA => Algorithm::EdDSA,
+      jsonwebtoken::Algorithm::HS256 => Algorithm::HS256,
+      jsonwebtoken::Algorithm::HS384 => Algorithm::HS384,
+      jsonwebtoken::Algorithm::HS512 => Algorithm::HS512,
+      jsonwebtoken::Algorithm::PS256 => Algorithm::PS256,
+      jsonwebtoken::Algorithm::PS384 => Algorithm::PS384,
+      jsonwebtoken::Algorithm::PS512 => Algorithm::PS512,
+      jsonwebtoken::Algorithm::RS256 => Algorithm::RS256,
+      jsonwebtoken::Algorithm::RS384 => Algorithm::RS384,
+      jsonwebtoken::Algorithm::RS512 => Algorithm::RS512,
+    }
+  }
+}
+
 impl Default for Algorithm {
   fn default() -> Self {
     Self::HS256

packages/jsonwebtoken/src/decode.rs

@@ -0,0 +1,10 @@
+use napi_derive::napi;
+
+use crate::header::Header;
+
+#[napi]
+pub fn decode_header(token: String) -> Header {
+  let result = jsonwebtoken::decode_header(&token);
+
+  result.unwrap().into()
+}

packages/jsonwebtoken/src/header.rs

@@ -73,6 +73,22 @@ impl From<&Header> for jsonwebtoken::Header {
   }
 }
 
+impl From<jsonwebtoken::Header> for Header {
+  #[inline]
+  fn from(value: jsonwebtoken::Header) -> Header {
+    Header {
+      algorithm: Algorithm::from(value.alg).into(),
+      content_type: value.cty.clone(),
+      json_key_url: value.jku.clone(),
+      key_id: value.kid.clone(),
+      x5_url: value.x5u.clone(),
+      x5_cert_chain: value.x5c.clone(),
+      x5_cert_thumbprint: value.x5t.clone(),
+      x5t_s256_cert_thumbprint: value.x5t_s256.clone(),
+    }
+  }
+}
+
 impl Header {
   #[inline]
   pub fn merge(self, other: Self) -> Self {

packages/jsonwebtoken/src/lib.rs

@@ -6,13 +6,15 @@ extern crate global_alloc;
 
 mod algorithm;
 mod claims;
+mod decode;
 mod header;
 mod sign;
 mod validation;
 mod verify;
 
 pub use algorithm::Algorithm;
 pub use claims::Claims;
+pub use decode::decode_header;
 pub use header::Header;
 pub use sign::{sign, sign_sync};
 pub use validation::Validation;