API access with client credentials (core functionality) (#16817)

* First stab

* Delivery API client credentials + a little refactor to ensure unique client IDs

* Introduce user type

* Support user type in the Management API

* Clean up TODOs

* Update API user last login date when issuing a token

* Better error reporting for mismatched user types

* Do not allow password change or reset for API users

* Update OpenApi.json

* Revert change

* Remove obsolete comment

* Make applicable classes abstract or sealed

* Review changes

* Add endpoint for retrieving all user client IDs

src/Umbraco.Core/Models/Membership/IUser.cs

@@ -39,6 +39,11 @@ public interface IUser : IMembershipUser, IRememberBeingDirty
     /// </summary>
     string? Avatar { get; set; }
 
+    /// <summary>
+    ///     The type of user.
+    /// </summary>
+    UserType Type { get; set; }
+
     void RemoveGroup(string group);
 
     void ClearGroups();

src/Umbraco.Core/Models/Membership/User.cs

@@ -41,6 +41,7 @@ public class User : EntityBase, IUser, IProfile
     private HashSet<IReadOnlyUserGroup> _userGroups;
 
     private string _username;
+    private UserType _type;
 
     /// <summary>
     ///     Constructor for creating a new/empty user
@@ -357,6 +358,13 @@ public class User : EntityBase, IUser, IProfile
         set => SetPropertyValueAndDetectChanges(value, ref _language, nameof(Language));
     }
 
+    [DataMember]
+    public UserType Type
+    {
+        get => _type;
+        set => SetPropertyValueAndDetectChanges(value, ref _type, nameof(Type));
+    }
+
     /// <summary>
     ///     Gets the groups that user is part of
     /// </summary>

src/Umbraco.Core/Models/Membership/UserType.cs

@@ -0,0 +1,7 @@
+namespace Umbraco.Cms.Core.Models.Membership;
+
+public enum UserType
+{
+    Default = 0,
+    Api
+}

src/Umbraco.Core/Models/UserCreateModel.cs

@@ -12,5 +12,7 @@ public class UserCreateModel
 
     public string Name { get; set; } = string.Empty;
 
+    public UserType Type { get; set; }
+
     public ISet<Guid> UserGroupKeys { get; set; } = new HashSet<Guid>();
 }