I'm currently working on a rust blockchain project and we are weeks until minimal test net, we have CLI wallet and network will support EVM on the real test net. We have rpc api and I would like to add section for metamask eg /api/metamask/ and what calls do I need for it. My crypto uses same secp256k1 as ethereum. Also I want to add a note that I have tried contacting metamask but they did not respond.
Supporting the standard web3 JSON RPC should be enough https://eth.wiki/json-rpc/API.
To known exactly what commands are required you could use ganache to log the command sends by Metamask to the ganache rpc server.
Ganache has a command line option
-v to log RPC requests and answers.