feat: add OIDC login with account linking

Add OpenID Connect as an alternative login method. Users can sign in
via an external identity provider (e.g., Authentik, Keycloak, Google).

- OIDC settings configured in admin UI (discovery URL, client ID/secret,
  redirect URI, button label, enable/disable toggle)
- PKCE-based authorization code flow with state and nonce validation
- Admin can manually link any user's OIDC identity (sub/issuer fields)
- Self-service linking: logged-in users can link/unlink their own account
- SSO button conditionally shown on login page when OIDC is enabled
- Username in header now clickable to open profile for all users
- Callback errors/success communicated via URL hash fragments

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "ezcheck",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "ezcheck",
-      "version": "0.1.0",
+      "version": "0.2.0",
       "dependencies": {
         "bcryptjs": "^3.0.3",
         "better-sqlite3": "^9.4.3",
@@ -14,6 +14,7 @@
         "express-session": "^1.19.0",
         "multer": "^2.1.1",
         "nodemailer": "^8.0.4",
+        "openid-client": "^5.7.1",
         "pdfkit": "^0.15.0"
       },
       "devDependencies": {
@@ -1391,6 +1392,15 @@
       "integrity": "sha512-xHjhDr3cNBK0BzdUJSPXZntQUx/mwMS5Rw4A7lPJ90XGAO6ISP/ePDNuo0vhqOZU+UD5JoodwCAAoZQd3FeAKw==",
       "license": "MIT"
     },
+    "node_modules/jose": {
+      "version": "4.15.9",
+      "resolved": "https://registry.npmjs.org/jose/-/jose-4.15.9.tgz",
+      "integrity": "sha512-1vUQX+IdDMVPj4k8kOxgUqlcK518yluMuGZwqlr44FS1ppZB/5GWh4rZG89erpOBOJjU/OBsnCVFfapsRz6nEA==",
+      "license": "MIT",
+      "funding": {
+        "url": "https://github.com/sponsors/panva"
+      }
+    },
     "node_modules/jpeg-exif": {
       "version": "1.1.4",
       "resolved": "https://registry.npmjs.org/jpeg-exif/-/jpeg-exif-1.1.4.tgz",
@@ -1417,6 +1427,18 @@
         "node": ">= 0.4"
       }
     },
+    "node_modules/lru-cache": {
+      "version": "6.0.0",
+      "resolved": "https://registry.npmjs.org/lru-cache/-/lru-cache-6.0.0.tgz",
+      "integrity": "sha512-Jo6dJ04CmSjuznwJSS3pUeWmd/H0ffTlkXXgwZi+eq1UCmqQwCh+eLsYOYCwY991i2Fah4h1BEMCx4qThGbsiA==",
+      "license": "ISC",
+      "dependencies": {
+        "yallist": "^4.0.0"
+      },
+      "engines": {
+        "node": ">=10"
+      }
+    },
     "node_modules/math-intrinsics": {
       "version": "1.1.0",
       "resolved": "https://registry.npmjs.org/math-intrinsics/-/math-intrinsics-1.1.0.tgz",
@@ -1654,6 +1676,15 @@
         "node": ">=0.10.0"
       }
     },
+    "node_modules/object-hash": {
+      "version": "2.2.0",
+      "resolved": "https://registry.npmjs.org/object-hash/-/object-hash-2.2.0.tgz",
+      "integrity": "sha512-gScRMn0bS5fH+IuwyIFgnh9zBdo4DV+6GhygmWM9HyNJSgS0hScp1f5vjtm7oIIOiT9trXrShAkLFSc2IqKNgw==",
+      "license": "MIT",
+      "engines": {
+        "node": ">= 6"
+      }
+    },
     "node_modules/object-inspect": {
       "version": "1.13.4",
       "resolved": "https://registry.npmjs.org/object-inspect/-/object-inspect-1.13.4.tgz",
@@ -1711,6 +1742,15 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
+    "node_modules/oidc-token-hash": {
+      "version": "5.2.0",
+      "resolved": "https://registry.npmjs.org/oidc-token-hash/-/oidc-token-hash-5.2.0.tgz",
+      "integrity": "sha512-6gj2m8cJZ+iSW8bm0FXdGF0YhIQbKrfP4yWTNzxc31U6MOjfEmB1rHvlYvxI1B7t7BCi1F2vYTT6YhtQRG4hxw==",
+      "license": "MIT",
+      "engines": {
+        "node": "^10.13.0 || >=12.0.0"
+      }
+    },
     "node_modules/on-finished": {
       "version": "2.4.1",
       "resolved": "https://registry.npmjs.org/on-finished/-/on-finished-2.4.1.tgz",
@@ -1741,6 +1781,21 @@
         "wrappy": "1"
       }
     },
+    "node_modules/openid-client": {
+      "version": "5.7.1",
+      "resolved": "https://registry.npmjs.org/openid-client/-/openid-client-5.7.1.tgz",
+      "integrity": "sha512-jDBPgSVfTnkIh71Hg9pRvtJc6wTwqjRkN88+gCFtYWrlP4Yx2Dsrow8uPi3qLr/aeymPF3o2+dS+wOpglK04ew==",
+      "license": "MIT",
+      "dependencies": {
+        "jose": "^4.15.9",
+        "lru-cache": "^6.0.0",
+        "object-hash": "^2.2.0",
+        "oidc-token-hash": "^5.0.3"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/panva"
+      }
+    },
     "node_modules/pako": {
       "version": "0.2.9",
       "resolved": "https://registry.npmjs.org/pako/-/pako-0.2.9.tgz",
@@ -2542,6 +2597,12 @@
       "resolved": "https://registry.npmjs.org/wrappy/-/wrappy-1.0.2.tgz",
       "integrity": "sha512-l4Sp/DRseor9wL6EvV2+TuQn63dMkPjZ/sp9XkghTEbV9KlPS1xUsZ3u7/IQO4wxtcFB4bgpQPRcR3QCvezPcQ==",
       "license": "ISC"
+    },
+    "node_modules/yallist": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/yallist/-/yallist-4.0.0.tgz",
+      "integrity": "sha512-3wdGidZyq5PB084XLES5TpOSRA3wjXAlIWMhum2kRcv/41Sn2emQ0dycQW4uZXLejwKvg6EsvbdlVL+FYEct7A==",
+      "license": "ISC"
     }
   }
 }