I am in the process of exposing a web interface to interact with a back-end Web3 Json Rpc compatible node, but it is necessary that I add additional parameters in the jsonrpc request before submitting it to the node.
I wish to use metamask as a user's keystore and signing interaction, however I cannot figure out how to ask metamask to simply sign the transaction json object with a meta mask account and returning the rawTransaction data (I can provide the chainId myself and all other needed parameters).
If I use the eth_sendTransaction, metamask created the rawTransaction data but submit it to the connected network and remove any additional parameter I would have passed in the request!
So I am looking at a eth_signTransaction that would be performed locally in metamask and not on the remote node. Does it exists ?
Thanks for the help