Password is not a common attribute. Indeed, in most of the cases, it is not stored in clear text in the backend (LDAP or database).
So to keep user password in session, you cannot just export the password variable in session. To bypass this, LL::NG can remember what password was given by user during authentication.
Attention
Go in Manager, General Parameters » Sessions » Store user password in session data and set to On.
To encrypt value in session, go to General Parameters » Sessions » Encrypt password in sessio and set to On.
User password is now available in $_password variable. For example, to send it in an header:
Auth-Password => $_password
Tip
For security reasons, the password is not shown in sessions explorer.