Kanboard and reverse-proxy authentication - php

Question

According the documentation (https://docs.kanboard.org/en/latest/admin_guide/reverse_proxy_authentication.html), i try to configure a simple authentication using the REVERSE_PROXY_USER_HEADER parameter.
For that, i set the parameters (data/config.php) like that !
define('REVERSE_PROXY_AUTH', true);
define('REVERSE_PROXY_USER_HEADER', 'REMOTE_USER');
define('REVERSE_PROXY_DEFAULT_ADMIN', 'admin');
define('REVERSE_PROXY_DEFAULT_DOMAIN', 'my-domain.fr');
I also change the apache2 log format for display my HTTP headers and i can see my 'user-name' in the corresponding log.
My HTTP request is this one :
Host: kbsso.my-domain.fr
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:66.0) Gecko/20100101 Firefox/66.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: fr,fr-FR;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
DNT: 1
Connection: keep-alive
Cookie: KB_SID=g6re22ivihojnle991idmo4vhh; KB_RM=4c14de632e17976bc894b9dd0f273c0415d0fef620b62b00bc8e782084775a97%7Cf47e8c6b8ab3721c60dd32fbc4ed129fedbeafc388ff66b3c9933e28c08d
Upgrade-Insecure-Requests: 1
REMOTE_USER: ex.valere.viandier
Pragma: no-cache
Cache-Control: no-cache
So, my problem is...
When REVERSE_PROXY_AUTH is set to true, the controller show me the login screen but if i try to loggin, i receive an "Access denied" HTML page.
When REVERSE_PROXY_AUTH is set to false, the controller show me the login screen and, using the same user account, i can access to kanboard.
The documentation say :
Your reverse proxy authenticates the user and send the username through a HTTP header.
Kanboard retrieve the username from the request
The user is created automatically if necessary
Open a new Kanboard session without any prompt assuming it’s valid
I try with existing and non-existing user but i have the same problem.
I try with v1.2.5, v1.2.8 but no way...
Do you know an issue ?
Thx a lot
Valère