feat: Add validation token endpoint

[bgins]

Summary

This pull request makes the following changes:

• Add solver validation token secret and expiration options
• Add solver validation token endpoint
• Add client validation token helper

We are adding a validation token endpoint to support our upcoming validation service.

Task/Issue reference

Closes: #486

Test plan

We have included a temporary commit (be58e61) to show a client request for a token. This temporary commit will be removed before merging this pull request.

Details

We have added SERVER_VALIDATION_TOKEN_SECRET and SERVER_VALIDATION_TOKEN_EXPIRATION solver server options. SERVER_VALIDATION_TOKEN_SECRET is required and does not have a default value. SERVER_VALIDATION_TOKEN_EXPIRATION defaults to a one week, but can be configured to another value in seconds.

The options can be configured through environment variables or CLI options:

./stack solver --server-validation-token-expiration 500
SERVER_VALIDATION_TOKEN_EXPIRATION=500 ./stack solver
./stack solver --server-validation-token-secret somesecret
SERVER_VALIDATION_TOKEN_SECRET=somesecret ./stack solver

Note that the SERVER_VALIDATION_TOKEN_SECRET is overridden by the key we have generated for local development:

lilypad/stack

Line 204 in be58e61

export SERVER_VALIDATION_TOKEN_SECRET=912dd001a6613632c066ca10a19254430db2986a84612882a18f838a6360880e

Comment this line to test.

Related issues or PRs

Epic: https://www.notion.so/lilypadnetwork/MVP-Validation-176155da99b5801ebeffc417f6b270c7

[hollygrimm]

I'd like to modify the value of sub, please see the specific comment for details.