test: set up test suite with Jest and MSW

[mantariksh]

Problem

Tests are good but we don't have them. Also, as we develop new SDKs, it will be useful to have consistent test cases as a reference point for implementation.

Solution

I considered two possible approaches:

1. Mock openid-client and check that we are interacting with it correctly
2. Mock network requests and ensure that the SDK returns the correct outputs

I went with approach 2 because 1 doesn't test for the possibility that openid-client introduces a bug or change in behaviour.

I chose msw to mock network requests instead of digging into the internals of openid-client and mocking whatever HTTP library they use (the native NodeJS HTTP API), as this allows us to stay agnostic to openid-client's internal implementation and just mock API responses.

Also, tests are now part of CI pipeline. See "Test" GitHub action.

Build changes
To include the test directory in the TS project but exclude it from the build pipeline, I set tsconfig.json to include tests, but created a new tsconfig.build.json which excludes tests and used it in npm run build.

New dev dependencies:

• jest, ts-jest, msw: for test framework in TypeScript
• jsonwebtoken: for generating testing data (sign ID token)
• eslint-plugin-jest: to write test nice nice

[gitguardian]

⚠️ GitGuardian has uncovered 3 secrets following the scan of your pull request.

Please consider investigating the findings and remediating the incidents. Failure to do so may lead to compromising the associated services or software components.

🔎 Detected hardcoded secrets in your pull request

GitGuardian id	Secret	Commit	Filename
6175562	Generic Private Key	0cd6f8d	test/mocks/mockClientKeys.json	View secret
6175563	RSA Private Key	0cd6f8d	test/mocks/mockPrivateKey.pem	View secret
6175564	Generic Private Key	0cd6f8d	test/mocks/mockPrivateKeyPkcs8.pem	View secret

🛠 Guidelines to remediate hardcoded secrets

1. Understand the implications of revoking this secret by investigating where it is used in your code.
2. Replace and store your secrets safely. Learn here the best practices.
3. Revoke and rotate these secrets.
4. If possible, rewrite git history. Rewriting git history is not a trivial act. You might completely break other contributing developers' workflow and you risk accidentally deleting legitimate data.

To avoid such incidents in the future consider

• following these best practices for managing and storing secrets including API keys and other credentials
• install secret detection on pre-commit to catch secret before it leaves your machine and ease remediation.

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[mantariksh]

@PrawiraGenestonlia thanks for the thoughtful review! left some of the comments open for discussion