Fix : certificate signed by unknown authority

README.md

@@ -105,6 +105,14 @@ Put your SSL certificate as `./volumes/web/cert/cert.pem` and the private key th
 no password as `./volumes/web/cert/key-no-password.pem`. If you don't have
 them you may generate a self-signed SSL certificate.
 
+#### Configure SSO with GitLab
+If you are looking for SSO with GitLab and you use self signed certificate you have to add the PKI chain of your authority in app because Alpine doesn't know him. This is required to avoid **Token request failed: certificate signed by unknown authority**
+
+For that uncomment this line and replace with the correct path of your PKI chain:
+```
+# - <path_to_your_gitlab_pki>/pki_chain.pem:/etc/ssl/certs/pki_chain.pem:ro
+```
+
 ### Starting/Stopping Docker
 
 #### Start

docker-compose.yml

@@ -35,6 +35,9 @@ services:
       - ./volumes/app/mattermost/plugins:/mattermost/plugins:rw
       - ./volumes/app/mattermost/client-plugins:/mattermost/client/plugins:rw
       - /etc/localtime:/etc/localtime:ro
+      # When you want to use SSO with GitLab, you have to add the cert pki chain of GitLab inside Alpine
+      # to avoid Token request failed: certificate signed by unknown authority (link: https://github.com/mattermost/mattermost-server/issues/13059)
+      # - <path_to_your_gitlab_pki>/pki_chain.pem:/etc/ssl/certs/pki_chain.pem:ro
     environment:
       # set same as db credentials and dbname
       - MM_USERNAME=mmuser