There is a Java API available so you can write a custom action or jsp. You may have to dig around to find the correct one for your Netweaver version.
https://help.sap.com/javadocs/nwce/ce71/se/com/sap/security/api/IUserAccount.html
I think there was a UME web service at one time but it wasn't supported and isn't available anymore.
Regards,
Christian