I recently paid for a 'proof of human' token (solving a Captcha) from Civic. It's stored as a 'gateway token' with 'gatekeepers' in my wallet. I've searched for 'gateway token' and 'gatekeeper' but not been able to find much documentation on these topics.
What are gateway tokens and gatekeepers?
A gateway token is a token used to control access to dApps.
On-chain applications require users to present a Gateway Token, which proves that they have been verified by a Gateway Provider to use the dApp. This token is tied to their wallet and is non-transferable.
Gateway tokens are issued by gatekeepers. A cluster of gatekeepers with similar rules for issuing gateway tokens are defined as a Gatekeeper Network.
The on-chain program chooses a gatekeeper network to trust, by adding its public key to a program account.
This library then validates that gateway tokens are issued by gatekeepers in this network and are valid.
More info available through the 'solana-gateway' docs: https://crates.io/crates/solana-gateway
