In PowerApps you can define a custom connector that uses environment variables in its OAuth security settings, but users running the app can't access the connector. After some testing Microsoft determined in case 2203090010000140 that use of environment variables this way is currently unsupportable and is a product limitation.
The request is to remove this limitation and support environment variables in the OAuth settings.
Custom connectors are the gateway between apps and REST APIs. This opens up the PowerApps world to using APIs beyond the standard connectors, something that is a significant need in business systems. Businesses also need to secure access to APIs, and OAuth securest option currently available in PowerApps custom connectors. Businesses also want to automate releases through pipelines and ALM without manual steps. Without environment variable support in custom connectors deployment has to be manual and less secure.