Extend JwtHeader to allow additional fields (#476)

* Extend JwtHeader to allow additional fields

* remove comment

* Change type DecodedJwt.header into a Record

src/index.d.ts

@@ -63,8 +63,8 @@ type SignerCallback = (e: Error | TokenError | null, token: string) => void
 type VerifierCallback = (e: Error | TokenError | null, payload: any) => void
 
 type DecodedJwt = {
-  header: { [key: string]: any },
-  payload: any,
+  header: Record<string, any>
+  payload: any
   signature: string
 }
 
@@ -80,7 +80,7 @@ declare function VerifierSync(token: string | Buffer): any
 declare function VerifierAsync(token: string | Buffer): Promise<any>
 declare function VerifierAsync(token: string | Buffer, cb: object): void
 
-export interface JwtHeader {
+export interface JwtHeader extends Record<string, any> {
   alg: string | Algorithm
   typ?: string | undefined
   cty?: string | undefined

test/types.spec.ts

@@ -3,7 +3,15 @@
 /* eslint-disable @typescript-eslint/no-unused-vars */
 /* eslint-disable @typescript-eslint/no-empty-function */
 
-import { createDecoder, createSigner, createVerifier, DecodedJwt, JwtHeader, TokenError, TokenValidationErrorCode } from '..'
+import {
+  createDecoder,
+  createSigner,
+  createVerifier,
+  DecodedJwt,
+  JwtHeader,
+  TokenError,
+  TokenValidationErrorCode
+} from '..'
 import { expectAssignable, expectNotAssignable, expectType } from 'tsd'
 
 // Signing
@@ -94,6 +102,24 @@ const signerOptions = {
 }
 expectAssignable<JwtHeader>(signerOptions.header)
 
+const signerOptionsCustomHeaders = {
+  header: {
+    alg: 'RS256',
+    typ: '',
+    cty: '',
+    crit: [''],
+    kid: '',
+    jku: '',
+    x5u: '',
+    'x5t#S256': '',
+    x5t: '',
+    x5c: '',
+    customClaim: 'my-custom-claim',
+    customClaim2: 'my-custom-claim2'
+  }
+}
+expectAssignable<JwtHeader>(signerOptionsCustomHeaders.header)
+
 const signerOptionsNoAlg = {
   header: {
     typ: '',