code: public String extractAccessToken(String authorization, String accessTokenInRequestParameters)
      {
          // Extract an access token from the value of Authorization header.
          String accessToken = BearerToken.parse(authorization);
  
          // If an access token was not found in Authorization header.
          if (accessToken == null)
          {
              // Use the value given via 'access_token' request parameter.
              accessToken = accessTokenInRequestParameters;
          }
  
          return accessToken;
      }
docs: Extract an access token from either {@code Authorization} header
  or request parameters.
  
  <p>
  The first argument expects a value of {@code Authorization} header
  that complies with <a href="http://tools.ietf.org/html/rfc6750"
  >RFC 6750</a> (Bearer Token Usage). If the argument contains an
  access token, this method returns the access token without checking
  the second argument.
  </p>
  
  <p>
  The second argument expects a value of {@code access_token}
  request parameter. The value of this argument is returned when
  the first argument does not contain an access token.
  </p>
  
  @param authorization
  A value of {@code Authorization} header whose scheme is
  Bearer. For example, {@code "Bearer SlAV32hkKG"}.
  
  @param accessTokenInRequestParameters
  A value of {@code access_token} request parameter.
  
  @return
  An access token.