http: prevent custom Authorization headers in redirects

... unless CURLOPT_UNRESTRICTED_AUTH is set to allow them. This matches how
curl already handles Authorization headers created internally.

Note: this changes behavior slightly, for the sake of reducing mistakes.

Added test 317 and 318 to verify.

Reported-by: Craig de Stigter
Bug: https://curl.haxx.se/docs/adv_2018-b3bf.html

lib/http.c

@@ -714,7 +714,7 @@ Curl_http_output_auth(struct connectdata *conn,
   if(!data->state.this_is_a_follow ||
      conn->bits.netrc ||
      !data->state.first_host ||
-     data->set.http_disable_hostname_check_before_authentication ||
+     data->set.allow_auth_to_other_hosts ||
      strcasecompare(data->state.first_host, conn->host.name)) {
     result = output_auth_headers(conn, authhost, request, path, FALSE);
   }
@@ -1636,6 +1636,14 @@ CURLcode Curl_add_custom_headers(struct connectdata *conn,
                   checkprefix("Transfer-Encoding:", headers->data))
             /* HTTP/2 doesn't support chunked requests */
             ;
+          else if(checkprefix("Authorization:", headers->data) &&
+                  /* be careful of sending this potentially sensitive header to
+                     other hosts */
+                  (data->state.this_is_a_follow &&
+                   data->state.first_host &&
+                   !data->set.allow_auth_to_other_hosts &&
+                   !strcasecompare(data->state.first_host, conn->host.name)))
+            ;
           else {
             CURLcode result = Curl_add_bufferf(req_buffer, "%s\r\n",
                                                headers->data);

lib/setopt.c

@@ -442,7 +442,7 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option,
      * Send authentication (user+password) when following locations, even when
      * hostname changed.
      */
-    data->set.http_disable_hostname_check_before_authentication =
+    data->set.allow_auth_to_other_hosts =
       (0 != va_arg(param, long)) ? TRUE : FALSE;
     break;
 

lib/urldata.h

@@ -1599,7 +1599,7 @@ struct UserDefined {
   bool http_keep_sending_on_error; /* for HTTP status codes >= 300 */
   bool http_follow_location; /* follow HTTP redirects */
   bool http_transfer_encoding; /* request compressed HTTP transfer-encoding */
-  bool http_disable_hostname_check_before_authentication;
+  bool allow_auth_to_other_hosts;
   bool include_header;   /* include received protocol headers in data output */
   bool http_set_referer; /* is a custom referer used */
   bool http_auto_referer; /* set "correct" referer when following location: */