add ADR#0008 describing decisions made in implementing Microsoft SSO/…

…auth, add How To for setting up related Azure application

doc/architecture/decisions/0003-testing-approach.md

@@ -1,4 +1,4 @@
-# 1. Testing Principles
+# 3. Testing Principles
 
 ## Status
 

doc/architecture/decisions/0008-authentication-with-microsoft.md

@@ -0,0 +1,48 @@
+# 8. User authentication via Microsoft SSO
+
+Date: 2024-10-31
+
+## Status
+
+Accepted
+
+## Context
+
+Previously, PlanX users could only log in to the editor using Google single sign on (SSO). This was true for OSL devs and end-users alike. Most councils run Microsoft, so we needed to add an additional option to authenticate via Microsoft instead.
+
+## Decisions
+
+We considered replacing the auth business logic wholesale with AWS Cognito, but this seemed like it would be a much more significant overhaul as compared with simply adding a new `passportjs` '[strategy](https://www.passportjs.org/concepts/authentication/strategies/)'.
+
+Since we already had a model strategy for Google, a principle decision which guided this work was to build a strategy for Microsoft which had parity with that existing solution. This also meant leveraging the existing method for a user to identify themselves to the client/editor, which is for the API to return a persistent `jwt` cookie after auth.
+
+### `passportjs`
+
+We considered a few strategies: [`passport-microsoft`](https://www.passportjs.org/packages/passport-microsoft/) didn't pass muster and [`passport-azure-ad`](https://www.passportjs.org/packages/passport-azure-ad/) was [deprecated](https://github.com/AzureAD/microsoft-identity-web/discussions/2405) (without replacement) by Microsoft, so we opted for building a custom solution using [OpenID Connect](https://openid.net/) (aka. OIDC, a layer on top of OAuth2 for which Microsoft has [good documentation](https://learn.microsoft.com/en-us/entra/identity-platform/v2-protocols-oidc)) with the [certified](https://openid.net/developers/certified-openid-connect-implementations/) [`openid-client`](https://www.passportjs.org/packages/openid-client/) strategy.
+
+### Auth flow
+
+OIDC provides for multiple '[authorisation flows](https://auth0.com/docs/get-started/authentication-and-authorization-flow)'. In our case the frontend, which is a public client, directs users to the API for auth purposes, which can store secrets. This enables us to use Hybrid Flow, rather than the more cumbersome Authorization Code Flow.
+
+### Logging out
+
+We also considered what happens when users who have authenticated via Microsoft SSO log out, either from PlanX, or from their Microsoft account more widely.
+
+In the former case, we simply delete the `jwt` as usual. For the latter case, there was the option of implementing a [front channel logout URL](https://learn.microsoft.com/en-us/entra/identity-platform/v2-protocols-oidc#what-is-a-front-channel-logout-url). Given the current setup, integrating this feature would have required a significant amount of work, and would also move us beyond parity with the Google solution, so we didn't deem it necessary at this time.
+
+## Consequences
+
+The upshot is that both devs and end-users can log into PlanX with any Microsoft email address (whether personal or belonging to/managed by an organisation).
+
+### ESM adoption
+
+With the implementationd described above, the API server has to fetch the [Microsoft OIDC config](https://login.microsoftonline.com/common/v2.0/.well-known/openid-configuration) on boot, which it does asynchronously. Observing this functionality would have required us to either refactor the codebase extensively, or write a [top-level](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await#top_level_await) `await`.
+
+The latter is much simpler and more elegant, but in turn requires that the API codebase is entirely ESM-compliant. This turned out to be a significant spike. Without going into detail, it prompted us to do the following (inter alia):
+
+- replace `ts-node-dev` with `tsx`
+- enforce the `verbatimModuleSyntax` [tsconfig option](https://www.typescriptlang.org/tsconfig/#verbatimModuleSyntax)
+- migrate our testing framework from Jest to Vitest
+- bump `passportjs` to latest version (a longstanding ticket)
+
+The happy byproduct of all this is a much more modern configuration of the API TypeScript setup, testing suite and dev framework.

doc/how-to/how-to-setup-azure-application.md

@@ -0,0 +1,19 @@
+# How to setup Azure application for Microsoft OIDC
+
+## Context
+
+One of the more complicated aspects of implementing the Microsoft single sign on via OpenID Connect (see ADR#0008) is setting up an appropriate application on Azure (Microsoft's cloud platform).
+
+We document the process here for posterity/future reproducibility.
+
+## Process 
+
+1. Start a new registration in the [App registrations](https://portal.azure.com/#view/Microsoft_AAD_RegisteredApps/ApplicationsListBlade) panel (this will automatically create a corresponding [Enterprise application](https://portal.azure.com/#view/Microsoft_AAD_IAM/StartboardApplicationsMenuBlade/~/AppAppsPreview))
+2. We will support account types ‘in any organizational directory’ (i.e. multitenant), *and* personal accounts
+3. Register the application as an SPA, with the following redirect URIs:
+    -  `https://api.editor.planx.uk/auth/microsoft/callback` (production)
+    -  `https://api.editor.planx.dev/auth/microsoft/callback` (staging)
+    -  `http://localhost/auth/microsoft/callback` (local development)
+3. Navigate to *Manage/Authentication*, and allow both access and ID tokens
+4. Go to *Manage/Certificates and secrets*, add a new client secret, and record the value - this is your `MICROSOFT_CLIENT_SECRET` environment variable
+5. Go to *Overview*, and copy the `Application (client) ID` - this is your `MICROSOFT_CLIENT_ID`