If the user does not need access to the AP -> Manage page at all, you could simply limit their role to a Monitoring or Audit user to prevent them from having access to the plain-text credentials. The option for hiding the credentials for all users can be enabled via a database command:
1. Log in to the AMP console as root directly or via SSH
2. Type db to access the database
[root@kelvin ~]# db
Welcome to psql 8.1.3, the PostgreSQL interactive terminal.
Type: \copyright for distribution terms
\h for help with SQL commands
\? for help with psql commands
\g or terminate with semicolon to execute query
\q to quit
3. Update the hide_secrets field
airwave=> update seas_config set hide_secrets=1;
4. Type \q to quit the database.
Once that field is toggled, the AMP will no longer display the AP credentials in the web interface.