Custom Extension Repository
Note
This section is only relevant for Classic mode installations, as Composer Mode installations use the download functionality of Composer.
TYPO3 provides functionality that connects to a different repository type
than the "official" TER (TYPO3 Extension Repository) to download third-party extensions.
The API is called "Extension Remotes". These remotes are adapters that allow
fetching a list of extensions via the 
        Listable or downloading
an extension via the 
        Extension.
It is possible to add new remotes, disable registered remotes or change the default remote.
Custom remote configuration can be added in the
Configuration/Services.yaml of the corresponding extension.
extension.remote.myremote:
  class: 'TYPO3\CMS\Extensionmanager\Remote\TerExtensionRemote'
  arguments:
    $identifier: 'myremote'
    $options:
       remoteBase: 'https://my_own_remote/'
  tags:
    - name: 'extension.remote'
      default: true
    Using 
        default: true, "myremote" will be used as the default remote.
Setting 
        default: true only works if the defined service
implements 
        Listable.
Please note that 
        \Vendor\ must implement
        Extension to be registered as remote.
To disable an already registered remote, 
        enabled: false can be set.
extension.remote.ter:
  tags:
    - name: 'extension.remote'
      enabled: false