Add OPDS 2 Authorization Code flow with PKCE

package.json

@@ -32,6 +32,9 @@
     "testFile": "cross-env JEST_TESTS=1 jest --config=jest.config.js --verbose --runInBand --bail=1 --no-cache ",
     "test:pdf-annotations:harness:install": "playwright install chromium",
     "test:pdf-annotations:harness": "playwright test --config=projects/pdf-annotations/harness/playwright.config.ts",
+    "start:opds-pkce-test-server": "node projects/opds-pkce-test-server/server.mjs",
+    "test:opds-pkce-test-server": "node --test projects/opds-pkce-test-server/server.test.mjs",
+    "test:opds-pkce": "cross-env JEST_TESTS=1 jest --config=jest.config.js --verbose --runInBand --bail=1 --no-cache test/main/network/opdsPkce.test.ts",
     "_NOT_NEEDED_postinstall_ReactARIAComponents": "node ./scripts/adobe-spectrum-react-aria-components-patch.js",
     "_NOT_NEEDED_postinstall": "npm run pinCompromisedColorPackage && npm run electron-build",
     "_NOT_NEEDED_pinCompromisedColorPackage": "(npm ls colors || echo \"NPM LS?\") && rimraf node_modules/electron-rebuild/node_modules/colors && rimraf node_modules/dir-compare/node_modules/colors",

projects/opds-pkce-test-server/README.md

@@ -0,0 +1,38 @@
+# OPDS Authorization Code with PKCE test server
+
+This dependency-free loopback server exercises the flow proposed in
+[opds-community/drafts#100](https://github.com/opds-community/drafts/issues/100).
+It is for local development only and does not authenticate real users.
+
+Run it from the repository root:
+
+```powershell
+npm run start:opds-pkce-test-server
+```
+
+Then add this protected catalog to Thorium:
+
+```text
+http://127.0.0.1:49152/opds/v2/catalog
+```
+
+The authentication document contains only the proposed flow type and its
+required `authenticate` and `refresh` links. The server expects the shared OPDS
+client ID `http://opds-spec.org/auth/client`, the callback `opds://authorize/`,
+and PKCE `S256`. The `refresh` link targets `/token`, which handles both the
+authorization-code exchange and refresh-token grant.
+
+Because this local server uses plain HTTP, only development and CI builds of
+Thorium accept its loopback endpoints. Production builds require HTTPS.
+
+Use a different port with an optional argument:
+
+```powershell
+node projects\opds-pkce-test-server\server.mjs 49153
+```
+
+Run its tests with:
+
+```powershell
+npm run test:opds-pkce-test-server
+```