allows override of asap key server in token utility

resources/prosody-plugins/token/util.lib.lua

 --- Returns the public key by keyID
 -- @param keyId the key ID to request
 -- @return the public key (the content of requested resource) or nil
-function Util:get_public_key(keyId)
+function Util:get_public_key(keyId,asapKeyServer)
+    if asapKeyServer == "" then
+        asapKeyServer = self.asapKeyServer)
+    end
     local content = cache:get(keyId);
     if content == nil then
         -- If the key is not found in the cache.
             end
             done();
         end
-        local keyurl = path.join(self.asapKeyServer, hex.to(sha256(keyId))..'.pem');
+        local keyurl = path.join(asapKeyServer, hex.to(sha256(keyId))..'.pem');
         module:log("debug", "Fetching public key from: "..keyurl);
 
         -- We hash the key ID to work around some legacy behavior and make
 -- @param session the current session
 -- @return false and error
 function Util:process_and_verify_token(session)
+    return self:process_and_verify_token_with_keyserver(session,"")
+end
+function Util:process_and_verify_token_with_keyserver(session,asapKeyServer)
+    if asapKeyServer == "" then
+        asapKeyServer = self.asapKeyServer
+    end
 
     if session.auth_token == nil then
         if self.allowEmptyToken then
     end
 
     local pubKey;
-    if self.asapKeyServer and session.auth_token ~= nil then
+    if asapKeyServer and session.auth_token ~= nil then
         local dotFirst = session.auth_token:find("%.");
         if not dotFirst then return nil, "Invalid token" end
         local header = json.decode(basexx.from_url64(session.auth_token:sub(1,dotFirst-1)));
         if kid == nil then
             return false, "not-allowed", "'kid' claim is missing";
         end
-        pubKey = self:get_public_key(kid);
+        pubKey = self:get_public_key(kid,asapKeyServer);
         if pubKey == nil then
             return false, "not-allowed", "could not obtain public key";
         end
 
     -- now verify the whole token
     local claims, msg;
-    if self.asapKeyServer then
+    if asapKeyServer then
         claims, msg = self:verify_token(session.auth_token, pubKey);
     else
         claims, msg = self:verify_token(session.auth_token, self.appSecret);