CMS login redirects to back to login I have an existing CMS website that seemingly has been working fine for several months.  Just recently we have lost the ability to access the admin portion of the site (the rest of the site works well).  To our knowledge, nothing has changed to make the site behave differently.

We have since set up our own dev box with identical code and it seems to behave the same way.  Works one day, next day we can't log in.  No errors in browser or log files.  Browser cache and cookies cleared.  Different browsers all work the same way.  You log in, it blinks a second, then redirects to login.  If wrong password entered, we get the wrong password error.  Even the database seems to show our login was good.

We have multiple environments on the original site, only the production environment has this issue.  Our second environment only has the production environment so i don't think they are conflicting.

Only thing i can think of is nginx cache but we don't cache the admin directories.  I don't see anything different in .htaccess that would do this.

Any ideas?
Sorry for answering my own question.  

Upon a suggestion from P&amp;T, we found that our Nginx configuration was removing the cookies when it cached the page. When we left the cookies in, we were able to log in.

We still don't know what changed to make the site suddenly not work, but at least the control panel is usable.