Github supports this out of the box – https://docs.github.com/en/code-security/secret-scanning/abo..., and recognizes tokens from a lot of services.
Mind you, your secrets need to have a distinctive format in order for this to work. Probably a distinctive prefix is enough.
An Unethical Life Pro-Tip (that the word is already out on anyway, so I don't feel too bad):
• The content of Github public repos is all continuously loaded (by Github themselves) as a public dataset into BigQuery — https://console.cloud.google.com/marketplace/details/github/....
• For about $500, you can use BigQuery to extract all matches of a particular regexp, from every file, in every commit, in every public Github repo.
Whether or not Github themselves use this to power their secret scanning, arbitrary third parties (benevolent or not) certainly can use it for such. And likely already do.
Also I'd hope that Google is scanning BigQuery queries for that abuse signal.
https://github.blog/changelog/2018-08-01-new-delay-public-ev...
Disclosure: I'm an ex-GitHub employee but was not involved in the secret scanning API.
Mind you, the Github dataset isn't the leak itself; the leak is the public repo that the user pushed their key to. The dataset just makes such searches scalable / cost-effective to third parties who aren't already indexing Github for some other reason.