Fix authentication sidecar eating all requests that start with "/login".

We need to use an exact match for our various URL handlers, so that we
do not inadvertently grab requests that were not targeted at us.

nginx/site.conf

@@ -9,16 +9,16 @@ server {
                 rewrite_by_lua_file /usr/local/share/lua/5.1/feide.lua;
         }
 
-        location /auth_proxy_callback {
+        location = /auth_proxy_callback {
                 rewrite_by_lua_file /usr/local/share/lua/5.1/callback.lua;
         }
 
-        location /logout {
+        location = /logout {
                 set $action 'logout';
                 rewrite_by_lua_file /usr/local/share/lua/5.1/auth.lua;
         }
 
-        location /login {
+        location = /login {
                 set $action 'login';
                 rewrite_by_lua_file /usr/local/share/lua/5.1/auth.lua;
         }