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By default, eXo Platform is case insensitive. You can configure it to become case sensitive through a parameter in exo.properties file:
exo.auth.case.insensitive, default value set to true.
If you set the exo.auth.case.insensitive to true this means that the username "user" is the same as "User" or "uSEr".
If it is set to false, this means that the user should take care of capital and minimal letters when typing the username.