Hide "username" field when HTTP authentication is enabled

In case if username is already known from HTTP request headers, there
is no sense to ask user to enter it again. This adds needUserForm
method to Authz class and modifies the authFormIfNeeded template to
hide the username field if not needed.

master/buildbot/status/web/authz.py

@@ -82,6 +82,18 @@ def needAuthForm(self, action):
             return True
         return False
 
+    def needUserForm(self, action):
+        """Does this action require an user form?"""
+        if action not in self.knownActions:
+            raise KeyError("unknown action")
+        if self.useHttpHeader:
+            # TODO: show the form when Authorization header is missing?
+            return False
+        cfg = self.config.get(action, False)
+        if cfg:
+            return True
+        return False
+
     def actionAllowed(self, action, request, *args):
         """Is this ACTION allowed, given this http REQUEST?"""
         if action not in self.knownActions:

master/buildbot/status/web/templates/forms.html

@@ -4,12 +4,12 @@
       <span class="label">Your username:</span>
       <input type="text" name="username"/>
     </div>
-  
+
     <div class="row">
       <span class="label">Your password:</span>
       <input type="password" name="passwd"/>
     </div>
-  {% else %}
+  {% elif authz.needUserForm(action) %}
     <div class="row">
       <span class="label">Your name:</span>
       <input type="text" name="username"/>

master/buildbot/test/unit/test_status_web_authz_Authz.py

@@ -171,6 +171,22 @@ def test_needAuthForm_callable(self):
         z = Authz(stopAllBuilds = lambda u : False)
         assert z.needAuthForm('stopAllBuilds')
 
+    def test_needUserForm_False(self):
+        z = Authz(forceBuild = False)
+        assert not z.needUserForm('forceBuild')
+
+    def test_needUserForm_Ture(self):
+        z = Authz(forceBuild = True)
+        assert z.needUserForm('forceBuild')
+
+    def test_needUserForm_http_False(self):
+        z = Authz(useHttpHeader = True, forceBuild = False)
+        assert not z.needUserForm('forceBuild')
+
+    def test_needUserForm_http_True(self):
+        z = Authz(useHttpHeader = True, forceBuild = True)
+        assert not z.needUserForm('forceBuild')
+
     def test_constructor_invalidAction(self):
         self.assertRaises(ValueError, Authz, someRandomAction=3)