[2.3] [Security] Add a getter for providers to the ChainUserProvider class

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes

I've got a use case where I need to check if any of the chained user providers implement a particular interface. This getter would really help with that.