[keycloak-user] How to store and search for (standardized?) user attributes?

Hi! We'd like to be able to store somewhat standard user attributes that complete the email, first and last name values that Keycloak 'natively' stores. Think of things like a date of birth, home/work address, phone number, etc. Additionally, we'd like to be able to find users based on a search query. We'd like to be able to answer questions like: "how many users live in London?" So far, we've found the user attributes, where we could store this information. That is a very generic solution though. Are there standardized attribute names, profiles, that we can use? A further challenge is that we'd like to be able to query the user base, based on attributes. We'd like to find people by address, by date of birth, etc. The REST API does have search functionality, but it doesn't look like you can find users by attribute value. Can anyone recommend a course of action here? Regards, Guus