http: Handle proxy authentication

Tested with both Basic and Digest authentication, and tested with
both proxy authentication and authentication for the requested
resource at the same time.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/httpauth.c

@@ -87,7 +87,7 @@ static void choose_qop(char *qop, int size)
 void ff_http_auth_handle_header(HTTPAuthState *state, const char *key,
                                 const char *value)
 {
-    if (!strcmp(key, "WWW-Authenticate")) {
+    if (!strcmp(key, "WWW-Authenticate") || !strcmp(key, "Proxy-Authenticate")) {
         const char *p;
         if (av_stristart(value, "Basic ", &p) &&
             state->auth_type <= HTTP_AUTH_BASIC) {