Thank for the report. Good to know that some users are starting to use this feature. Since your problem definitely requires to change code, please open an issue at GitHub.
Edit: Please create two separate issues: one for the visibility toggle and one for storing API keys for different providers.
By the way, keys are NOT always visible in plain text:
You do NOT want to send your API key from provider A to provider B, otherwise provider B could abuse your personal API key to access the service from provider A. Switching providers loses previous provider’s key is correct behaviour. What is needed is storage for different providers.