Force mtlsFetch binding.

Author: dompuiu

src/__tests__/getMtlsFetch.test.js

@@ -25,12 +25,14 @@ describe('getMtlsFetch', () => {
   it('should return the MTLS fetch function when the binding exists', () => {
     // Arrange
     mockEnv[MTLS_BINDING] = { fetch: mockFetch };
+    const boundMockFetch = mockFetch.bind(mockEnv[MTLS_BINDING]);
+    mockFetch.bind = vi.fn().mockReturnValue(boundMockFetch);
 
     // Act
     const result = getMtlsFetch(mockEnv);
 
     // Assert
-    expect(result).toBe(mockFetch);
+    expect(result).toBe(boundMockFetch);
   });
 
   it('should return a function that throws an error when the binding does not exist', () => {

src/getMtlsFetch.js

@@ -13,7 +13,9 @@ import { MTLS_BINDING } from './constants.js';
 
 export default (env) => {
   if (env && env[MTLS_BINDING]) {
-    return env[MTLS_BINDING].fetch;
+    // We need the binding here, otherwise the worker will throw an error:
+    // TypeError: Illegal invocation: function called with incorrect `this` reference.
+    return env[MTLS_BINDING].fetch.bind(env[MTLS_BINDING]);
   }
 
   return () => {