Even where there is, there isn't a standard "put this in the password field" API. You'd need to modify both apps to cooperate, which is basically a no-go unless you control both.

But I would love such an API, for reasons like this. Clipboard / custom keyboard / etc are horrific alternatives when you could e.g. do an oauth-like app-redirect. Both sides can validate each other, and the user just has to hit yes/no/choose the account.