Keycloak user attributes with multiple values (list)

Question

I'm having a Keycloak use case where single user may have multiple customer numbers. These customer numbers would need to be sent to service provider / client and also be easily updated by administrators. Some users may have hundreds of customer numbers. Currently I'm using single user attribute named "customerNumbers" where the customer numbers are separated by comma but I'd like:

1. To offer the administrators possibility to see each customer number in its own field
2. To send the customer numbers as an JSON array instead of comma separated claim

So instead of this:

I'd like something like this:

And instead of this

"customers": {
"customerNumbers": "140661,140662"
},

I'd like something like this:

"customers": [
    {"customerNumber": "140661"},
    {"customerNumber": "140662"}
],

How should one approach this kind of situation?

Answer 1

Keyclaok use a custom format to save multiple value in the same field by separating multiple value with ##

key: customerNumbers      value: 140661##140662

if you want to show that field on your jwt access token you can do it by creating a client scope -> protocol mapper (user attribute) for custom attribute making sure to set multivalued on

set custom attribute on protocol mapper:

After that you can add those mapper to your client so it will appear on your access token

set custom attribute on jwt token: