http call response header returning null in angular 2
<p><strong>IOnic serve case:</strong>
when i run <strong>ionic serve</strong> http call return null in response header. i need headers to send in every next call for secure authentication. but Api returning null in response header when i call login http call.</p>

<p><strong>Ionic run android case:</strong>
 But another case is when i run <strong>ionic run android</strong>  it give me response header in login call but right after the login call when i call next http call it returns null in response header of next call.</p>

<p><strong>Here is my Login code:</strong> </p>

<pre><code> Login(email, password) {

        let body = JSON.stringify({email: email, password: password});
        //HTTP POST CALL FOR LOGIN 
        return this.http.post(this.LOGIN_URL, body, {headers: this.contentHeader}).subscribe(response =&gt; {

            if (response) {

                console.log('in login if');
                console.log(response.headers.get('uid'));
                console.log(response.headers.get('client'));
                console.log(response.headers.get('access-token'));

          this.uid = response.headers.get('uid');
          this.client =  response.headers.get('client');
          this.access_token =  response.headers.get('access-token');

//saving header for next call
  Save_Header(this.access_token, this.client, this.uid );


            } else{
              // login failed
              console.log("coming in........");
              this.error = 'Something went wrong';
              //  this.loading = false;
            }
    }
</code></pre>

<p><strong>Here is function which saving headers for next call:</strong></p>

<pre><code>Save_Header(access_token,client, uid){
        this.contentHeader.append('access-token', access_token);
        this.contentHeader.append('client', client);
        this.contentHeader.append('uid', uid);
       //console.log(this.contentHeader);
    }
</code></pre>

<p><strong>function for getting header for next call:</strong></p>

<pre><code>   Get_Header(){
    return this.contentHeader;
}
</code></pre>

<p><strong>Next http call:</strong></p>

<pre><code>Get_All_Delivered_orders(){
        console.log("in userservice all delivered orders")
        console.log(this.Get_Header());
       return this.http.get(URL,{headers: this.Get_Header()});// getting saved headers
    }
</code></pre>

<p>what will be the problem ,in implementation or in Api?
please guide thanks!</p>