feat: add AUTH_OIDC_NAME_CLAIM env variable

[Meierschlumpf]

Describe the feature you'd like to request

For Synology SSO and probably some other SSO providers the preferred_username property does not exist, because they do not completely follow the OIDC standard. For those users that use those providers it would be beneficial to have this env variable to override the property.

Additional information

profile(profile) {
  return {
    id: profile.sub,
    // Use the name as the username if the preferred_username is an email address
    name:  env.AUTH_OIDC_NAME_CLAIM ? profile[env.AUTH_OIDC_NAME_CLAIM] : profile.preferred_username.includes("@") ? profile.name : profile.preferred_username,
    email: profile.email,
    provider: "oidc",
  };
},

Originally posted in discord get-help post