Core Library Request: Crypto Shim

[southpolesteve]

Cosmos currently needs these platform crypto functions in both browser and node:

• SHA1
• HMAC-256
• atob

We currently use crypto-hash but it does not support HMAC256 and uses syntax incompatible with Edge. I propose the development of a new core library that shims these and any other required crypto functions for azure SDK packages.

cc @bterlson

[bterlson]

/cc @schaabs @jonathandturner

[joheredi]

There are 2 main things behind this issue

1. Cosmos is broken in Edge because crypto-hash uses incompatible syntax (such as spread) and features (such as 'SHA-1' with SubtleCrypto.digest())

2. Cosmos uses crypto-js for signing headers and we'd like to remove the dependency on it.

For fixing (1), I spoke with @southpolesteve and it seems like we should be able to use another algorithm (maybe SHA256). This hashing logic can be hosted within the Cosmos repo and drop the dependency on crypto-hash

For (2) 2 things need to happen
a) Move cosmos-sign into Cosmos repo
b) Drop the dependency on crypto-js and shim HMAC256

atob requirement has been addressed by this merge

@southpolesteve please feel free to fill in if I missed anything

/cc @ramya-rao-a @bterlson

[joheredi]

Fixed with #5493