title: Spring Rest template overwriting Authorization header value
body: <p>I am making rest call like below:</p>
  
  <pre><code>REST_TEMPLATE.exchange(
          external_rest_url,
          HttpMethod.POST,
          new HttpEntity&lt;&gt;(dto, getHeaders()),
          Map.class)
  </code></pre>
  
  <p>and my headers are as below:</p>
  
  <pre><code>private HttpHeaders getHeaders() {
      HttpHeaders headers = new HttpHeaders();
      headers.setAccept(Collections.singletonList(MediaType.APPLICATION_JSON));
      headers.setContentType(MediaType.APPLICATION_JSON);
      headers.set("User-Agent","Spring's RestTemplate");
      headers.set(HttpHeaders.AUTHORIZATION, "some value");
      return headers;
  }
  </code></pre>
  
  <p>when I run my code the header <code>HttpHeaders.AUTHORIZATION</code> is getting replaced with undefined</p>
  
  <p>See request header in snapshot below from network logs:
  <a href="https://i.stack.imgur.com/emouu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/emouu.png" alt="enter image description here"></a></p>
  
  <p>Do anyone know why spring is behaving like this or specifically <code>spring-web:5.0.5</code> jar. I tried changing the version of jar as well but result is same.</p>
  
  <p>Springboot version I use is <code>2.0.x</code>.</p>