An administrative client in OA4MP is a client that is authorized to create standard OAuth 2 clients. A standard OAuth client is one which gets tokens, etc. Administrative clients can be requested via a specific endpoint, usually ../oauth2/admin-client. It should be stressed that administrative clients are not part of any OAuth standard and are therefore outside the requirements for standard OAuth clients. The default registration screen looks like this:
Note that once this is submitted, it must be approved. Once your admin client has been approved, you may then create standard clients which are automatically approved on creation.
The most common use of an administrative client is the dynamic registration of standard clients. There are two general methods for this, the first is the native OA4MP client management protocol and the second is an implementation of RFCs 7591 and 7592 allowing for dynmaic client registration. The OA4MP protocol preceeded the RFCs by quite a while and both are generally supported on any standard OA4MP server. An advantage of the OA4MP protocol is that clients may specify additional configuration for native OA4MP tools, such as scripting for custom claim sources, which generic OIDC clients do not have.
Admin clients allows an institution to create customized clients each with their own configuration for open authorization. An example would be a COManage instance which could set up (a) specific client(s) for use by every virtual organization it creates.