You use the environment variable with a format ES_ESM_IDPW_CASE=xy, where "x" is the folding option for user ID, and "y" the option for password. The settings for "x" and "y" are:
When this environment variable is set, Enterprise Server will make only one attempt to identify a user, presenting the user ID and password as-is (M), folded to uppercase (U) or folded to lowercase(L). If this environment variable is not set, the legacy Enterprise Server behavior will be used.
For CICS legacy behavior, the user ID and password are used as given, and subject to any uppercase translation configuration of the sign-on transaction or terminal characteristics.
For ESMAC and IMS legacy behavior, there is potentially more than one authentication attempt. First, the user ID and password are used as given. If the authentication fails, the user ID is folded to uppercase and the authentication re-tried. If this fails as well, both the user ID and the password are folded to uppercase and the authentication re-tried.