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Login into backend not possible. Blank white page and 'Invalid challenge value' error

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I just put up a site on a hosting service that I didn't use before (strato.de). As always in those cases some things just won't work.

Right now I can not log into the backend of the site.

When calling the backend via https://www.mysite.com/processwire (not the actual URL of my site) I get a blank white page without any content.

When turning the debug mode on this login page looks normal. But after logging in again all I see is a blank white page.

In the session log I get a 'Invalid challenge value' error. The wire-challenge cookie is indeed missing, I can confirm hat.
However the session log also says "Successful login for 'admin'".

I've searched the board and found a few threads about this problem but none of the solutions work for me. Even turning the sessionChallenge off in the config does nothing:

$config->sessionChallenge = false;




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Another thing I discovered is that the redirect to the "URL with Slash at the end" does not work for the back-end login. For all other pages in the frontend it does.

When calling: https://www.mysite.com/processwire I get a blank page. 

In that case you normally get redirected to the same URL but with a slash at the end:


This URL shows the login page. But after logging in I get a new blank page...

In my local dev environment everything is working fine and I never had this problem before on other hosting providers.

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So finally I uploaded the website into my own personal webspace to see if the login works - it does.

So I guess it is some kind of .htaccess or php.ini (black) magic that is missing on the strato.de server. I am looking forward to see if somebody has a clue about this. 😑

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I was able to solve the problem. After logging into the backend and getting the blank admin page I discovered a log entry inside the tracy debugger log.

There was an issue in my /site/ready.php file that threw an error:

PHP Warning: Cannot modify header information - headers already sent by

That error was caused by some spaces behind the closing ?> Tag inside the ready.php.
I am using this same ready.php file on multiple other websites and it never made me any trouble though.

I find the fact weird that this error is only provoked when trying to log into the backend. Anyhow I am glad that this is solved now.

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that's why it is strongly advised not to use closing php tags for php only files, a simple space after the closing tag is considered as an ouput and if it occurs before any php header il will return an error 🙂

in case it may be useful

have a nice day

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