It’s a bad practice to hard-code script logins in your scripts or components. SeLite helps you to make it flexible, but it can’t do all the work for you.
If you use Firefox password store and you’ve saved the web application passwords, the script can access them via SeLiteMisc.loginManagerPassword(). You just need to configure/store the username(s) - see options below.
Beware that Firefox recovers the passwords as plain text. So they are only as safe as your home folder (which contains your Firefox profile).
If you have a short set of roles or username placeholders, of fixed length, which you want to be configurable, you could have a separate Settings field for each and configure the username through it. If you don’t use Firefox password store, then store the passwords in another set of fields - one for each such role.
So, for each role or username placeholder, you create one or two instances of SeLiteSettings.Field.String.
If you just want to configure one choice from a fixed list of credentials, then use single-valued SeLiteSettings.Field.Choice.String. The keys can be passwords and the values are usernames (displayed in SettingsInterface). (The passwords must be different across those usernames). If using Firefox password store, then Field.Choice.String keys and values can be the same - just usernames.
This uses SeLiteSettings.Field.FixedMap, which provides multivalued freetype fields with a fixed keyset. The keys hard-coded in the Settings module definition. The keys serve as symbolic placeholders for roles or usernames. The values can be the actual usernames, entered as freetype. If you don’t involve Firefox password store then have a second field with the same keyset, and enter the passwords as values of this field.
Frameworks can add keys to fields of class SeLiteSettings.Field.FixedMap. One such field is ‘extensions.selite-settings.common.roles’. Then they benefit from common functionality like SeLiteSettings.roleToUser(). See InstallFramework > Load and configure the framework.
If your scripts create/update user passwords, see GeneralFramework > Preserving special values in script DB.
The scripts contain rolenames or username placeholders - thus you don’t want to change them frequently. So there is no need to have the roles or username placeholders editable via GUI interface; it’s enough to have them hardcoded in the config field definition.
A more flexible option could be to use two or three multi-valued instances of SeLiteSettings.Field.String. The first one would list the role names or username placeholders and the second would contain the actual respective usernames (in the respective order). The third would be for passwords (again, in the respected order) - unless you use Firefox password store. Such paired lists would be flexible, but quite fragile to manage.
Anyway, this wouldn’t work out of the box, since multivalued SeLiteSettings.Field freetype values get sorted automatically. Also, preferences API doesn’t guarantee an order of fields. So they would have to be indexed by an auto-generated sequential key.
SeLite Settings doesn’t have any dictionary-like freetype field, which would let you enter pairs of keys (e.g. usernames) and values (e.g. passwords) in the browser. This is not trivial to add to the current implementation, due to its existing complexity and the awkwardness of dealing with Mozilla XUL.