By default in OWA 2010 if a user's password has expired they are told the username or password is invalid. They are unable to reset the password in OWA. This might be a pain when the passwords expire in the summer holidays. If you have SP1 + installed on the server users will be able to reset expired passwords before they login. All you have to do is make the following registry changes on all of your CAS servers.

1. 
   
2. Log on to the Client Access server.
   
3. Start Registry Editor (regedit).
   
4. Locate the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchange OWA.
   
5. Create the following DWORD value if it doesn't already exist: ChangeExpiredPasswordEnabled. The value type will be REG_DWORD.
   
6. Set the value of ChangeExpiredPasswordEnabled to 1.
   
7. Exit Registry Editor.
   

You will need to reset your IIS services.