As JIRA will depend on database whether to be case sensitive or insensitive, JIRA login for case sensitive database (eg. Postgres) will be case sensitive as well. To make the login page case insensitive, there are two files that need to be modified:
<jira-install>\atlassian-jira\WEB-INF\classes\templates\jira\dashboard\macros.vmwhich control the loginform at the dashboard page (eg. http://localhost:8085/secure/Dashboard.jspa). Modify the file as below
<jira-install>\atlassian-jira\includes\loginform.jspwhich control the loginform in the middle (eg. http://localhost:8085/login.jsp?os_destination=%2Fbrowse%2FTST-1). Modify the file as below Restart JIRA after the modification. If it does not take effect, delete the work directory and restart JIRA.