Phase 2: Authentication scaffolding

- Add JWT Bearer auth to ASP.NET (authority/audience from AUTH__AUTHORITY / AUTH__AUDIENCE config)
- Add KnownUserMiddleware: upserts KnownUser and resolves pending shares on each authenticated request
- Add MeController as a guarded test endpoint (/api/me)
- Add oidc-client-ts + react-router-dom to client
- Create AuthContext/AuthProvider with login, logout, token storage
- Create AuthGuard component protecting all budget routes
- Add stub /callback page for OIDC redirect handling
- Wire up all routes in App.tsx with SPA routing structure

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Budget.Client/package-lock.json

@@ -8,8 +8,10 @@
       "name": "budget-client",
       "version": "0.0.0",
       "dependencies": {
+        "oidc-client-ts": "^3.5.0",
         "react": "^19.2.5",
-        "react-dom": "^19.2.5"
+        "react-dom": "^19.2.5",
+        "react-router-dom": "^7.14.2"
       },
       "devDependencies": {
         "@eslint/js": "^10.0.1",
@@ -1306,6 +1308,19 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/cookie": {
+      "version": "1.1.1",
+      "resolved": "https://registry.npmjs.org/cookie/-/cookie-1.1.1.tgz",
+      "integrity": "sha512-ei8Aos7ja0weRpFzJnEA9UHJ/7XQmqglbRwnf2ATjcB9Wq874VKH9kfjjirM6UhU2/E5fFYadylyhFldcqSidQ==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=18"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/express"
+      }
+    },
     "node_modules/cross-spawn": {
       "version": "7.0.6",
       "resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-7.0.6.tgz",
@@ -1837,6 +1852,15 @@
         "node": ">=6"
       }
     },
+    "node_modules/jwt-decode": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/jwt-decode/-/jwt-decode-4.0.0.tgz",
+      "integrity": "sha512-+KJGIyHgkGuIq3IEBNftfhW/LfWhXUIY6OmyVWjliu5KH1y0fw7VQ8YndE2O4qZdMSd9SqbnC8GOcZEy0Om7sA==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/keyv": {
       "version": "4.5.4",
       "resolved": "https://registry.npmjs.org/keyv/-/keyv-4.5.4.tgz",
@@ -2204,6 +2228,18 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/oidc-client-ts": {
+      "version": "3.5.0",
+      "resolved": "https://registry.npmjs.org/oidc-client-ts/-/oidc-client-ts-3.5.0.tgz",
+      "integrity": "sha512-l2q8l9CTCTOlbX+AnK4p3M+4CEpKpyQhle6blQkdFhm0IsBqsxm15bYaSa11G7pWdsYr6epdsRZxJpCyCRbT8A==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "jwt-decode": "^4.0.0"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/optionator": {
       "version": "0.9.4",
       "resolved": "https://registry.npmjs.org/optionator/-/optionator-0.9.4.tgz",
@@ -2364,6 +2400,44 @@
         "react": "^19.2.5"
       }
     },
+    "node_modules/react-router": {
+      "version": "7.14.2",
+      "resolved": "https://registry.npmjs.org/react-router/-/react-router-7.14.2.tgz",
+      "integrity": "sha512-yCqNne6I8IB6rVCH7XUvlBK7/QKyqypBFGv+8dj4QBFJiiRX+FG7/nkdAvGElyvVZ/HQP5N19wzteuTARXi5Gw==",
+      "license": "MIT",
+      "dependencies": {
+        "cookie": "^1.0.1",
+        "set-cookie-parser": "^2.6.0"
+      },
+      "engines": {
+        "node": ">=20.0.0"
+      },
+      "peerDependencies": {
+        "react": ">=18",
+        "react-dom": ">=18"
+      },
+      "peerDependenciesMeta": {
+        "react-dom": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/react-router-dom": {
+      "version": "7.14.2",
+      "resolved": "https://registry.npmjs.org/react-router-dom/-/react-router-dom-7.14.2.tgz",
+      "integrity": "sha512-YZcM5ES8jJSM+KrJ9BdvHHqlnGTg5tH3sC5ChFRj4inosKctdyzBDhOyyHdGk597q2OT6NTrCA1OvB/YDwfekQ==",
+      "license": "MIT",
+      "dependencies": {
+        "react-router": "7.14.2"
+      },
+      "engines": {
+        "node": ">=20.0.0"
+      },
+      "peerDependencies": {
+        "react": ">=18",
+        "react-dom": ">=18"
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     "node_modules/rolldown": {
       "version": "1.0.0-rc.17",
       "resolved": "https://registry.npmjs.org/rolldown/-/rolldown-1.0.0-rc.17.tgz",
@@ -2421,6 +2495,12 @@
         "semver": "bin/semver.js"
       }
     },
+    "node_modules/set-cookie-parser": {
+      "version": "2.7.2",
+      "resolved": "https://registry.npmjs.org/set-cookie-parser/-/set-cookie-parser-2.7.2.tgz",
+      "integrity": "sha512-oeM1lpU/UvhTxw+g3cIfxXHyJRc/uidd3yK1P242gzHds0udQBYzs3y8j4gCCW+ZJ7ad0yctld8RYO+bdurlvw==",
+      "license": "MIT"
+    },
     "node_modules/shebang-command": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/shebang-command/-/shebang-command-2.0.0.tgz",