After installing your certificate a browser or app may prompt you for a password. It may look like the examples below:
In most cases the keychain name that is being prompted for is the one called "login".
To get past this message please put your Device's login password or login keychain password (if different then your computer login password). The login prompt may apear multiple times. To prevent the prompts from appearing in the future, please use the button that says "always allow" after inputing your login password.
You can read more about what Keychain is and it's function from Apple's website.