Ability to sign with AWS CloudHSM/Azure KeyVault/other

[Ivshti]

AWS CloudHSM (or similar) makes sense, since the validator demands more security and benefits from multiple options

Implementing an Ethereum provider and plugging into ethers.js is probably the way to go

See this StackExchange thread

See also:

• Azure-based solution: https://tomislav.tech/2018-01-31-ethereum-keyvault-generating-keys/
• provider: https://github.com/tmarkovski/ethereumjs-tx-keyvault
• Hashicorp Vault-based solution: https://www.hashicorp.com/blog/using-vault-to-build-an-ethereum-wallet/

Keep in mind, some HSM solutions are expensive, with CloudHSM being around ~12k per year; with Azure, you pay by the tx, and only 5$ per month to retain a EC key