Feature request: pure parser

[chidg]

For the extension, we generally follow a practice of avoiding cryptographic operations on the front end as much as possible for performance reasons, and also to avoid bundle size blowout. Some of the @polkadot/util-crypto utilities use large wasm blobs and increase build size and script loading time considerably. Over time, we've reduced our use of these utilities on the front end and plan to remove them entirely.

For integration with the extension, we would love to see a version of SiwsMessage which would not import any cryptographic modules like those from @polkadot/util-crypto or @azns/resolver-core. As a suggestion, it could be structured so that users of the API could pass in their own verification methods - then we could call the existing utilities on the extension backend to verify - alternatively, since we don't need currently use those methods, we would be happy with a base SiwsMessage class without them.