Accessing response header from Angular

I'm having trouble reading the custom response headers from Angular. My Angular code looks like this,

 testBackEndResponse() {
return this.http.post(
  "backendApiUrl",
  null,
  { observe: 'response', responseType: 'text' }
);

}

Reading the response

this.service
  .testBackEndResponse()
  .pipe(takeUntil(this.destroy$))
  .subscribe((resp) => {
    const keys = resp.headers.get('authorization');

});

Backend Node Azure Function Code

const httpTrigger: AzureFunction = async function (

context: Context, req: HttpRequest ): Promise { var params = req.params;

context.res.status = 200;
context.res.headers = {
  "Access-Control-Expose-Headers":
    "authorization",
  "Access-Control-Allow-Origin": "*",
  "authorization": "test token"
};

};

Even after exposing I still get "Content-Type" header only to the angular. Any reason?