src/trx-client/trx-frontend/trx-frontend-http/assets/web/generated/app.js

@@ -6066,6 +6066,7 @@ async function refreshUserManagement() {
   const list = requiredElement("user-list");
   try {
     const users = await listUsers();
+    const adminCount = users.filter((user) => user.role === "admin").length;
     list.replaceChildren(...users.map((user) => {
       const row = document.createElement("div");
       row.className = "sch-row";
@@ -6082,6 +6083,9 @@ async function refreshUserManagement() {
         option.selected = user.role === value;
         role.append(option);
       }
+      const isOnlyAdmin = user.role === "admin" && adminCount === 1;
+      role.disabled = isOnlyAdmin;
+      if (isOnlyAdmin) role.title = "The final administrator cannot be demoted";
       const password = document.createElement("input");
       password.type = "password";
       password.placeholder = "New password";
@@ -6100,7 +6104,8 @@ async function refreshUserManagement() {
       remove.type = "button";
       remove.textContent = "Remove";
       remove.className = "danger";
-      remove.disabled = user.username === authUsername;
+      remove.disabled = user.username === authUsername || isOnlyAdmin;
+      if (isOnlyAdmin) remove.title = "The final administrator cannot be removed";
       remove.addEventListener("click", async () => {
         if (await window.trxUi.confirm({ title: "Remove user?", message: `Remove ${user.username} and revoke their sessions?`, confirmLabel: "Remove", danger: true })) {
           await runUserOperation(() => deleteUser(user.username));

src/trx-client/trx-frontend/trx-frontend-http/frontend/src/app.ts

@@ -5070,6 +5070,7 @@ async function refreshUserManagement() {
   const list = requiredElement("user-list");
   try {
     const users = await listUsers();
+    const adminCount = users.filter(user => user.role === "admin").length;
     list.replaceChildren(...users.map((user) => {
       const row = document.createElement("div");
       row.className = "sch-row";
@@ -5082,6 +5083,9 @@ async function refreshUserManagement() {
       for (const value of ["user", "admin"] as AuthRole[]) {
         const option = document.createElement("option"); option.value = value; option.textContent = value === "admin" ? "Admin" : "User"; option.selected = user.role === value; role.append(option);
       }
+      const isOnlyAdmin = user.role === "admin" && adminCount === 1;
+      role.disabled = isOnlyAdmin;
+      if (isOnlyAdmin) role.title = "The final administrator cannot be demoted";
       const password = document.createElement("input");
       password.type = "password"; password.placeholder = "New password"; password.autocomplete = "new-password"; password.className = "auth-input"; password.minLength = 8;
       const save = document.createElement("button"); save.type = "button"; save.textContent = "Save";
@@ -5091,7 +5095,8 @@ async function refreshUserManagement() {
         await runUserOperation(() => updateUser(user.username, changes));
       });
       const remove = document.createElement("button"); remove.type = "button"; remove.textContent = "Remove"; remove.className = "danger";
-      remove.disabled = user.username === authUsername;
+      remove.disabled = user.username === authUsername || isOnlyAdmin;
+      if (isOnlyAdmin) remove.title = "The final administrator cannot be removed";
       remove.addEventListener("click", async () => {
         if (await window.trxUi.confirm({ title: "Remove user?", message: `Remove ${user.username} and revoke their sessions?`, confirmLabel: "Remove", danger: true })) {
           await runUserOperation(() => deleteUser(user.username));

src/trx-client/trx-frontend/trx-frontend-http/src/auth.rs

@@ -1201,11 +1201,31 @@ mod tests {
         );
         let request = aw_test::TestRequest::delete()
             .uri("/auth/users/alice")
-            .insert_header((actix_web::http::header::COOKIE, admin_cookie))
+            .insert_header((actix_web::http::header::COOKIE, admin_cookie.clone()))
             .to_request();
         assert_eq!(
             aw_test::call_service(&app, request).await.status(),
             actix_web::http::StatusCode::OK
         );
+
+        // Once only one administrator remains, neither API operation may
+        // leave the database without an administrator.
+        let request = aw_test::TestRequest::patch()
+            .uri("/auth/users/admin")
+            .insert_header((actix_web::http::header::COOKIE, admin_cookie.clone()))
+            .set_json(serde_json::json!({"role":"user"}))
+            .to_request();
+        assert_eq!(
+            aw_test::call_service(&app, request).await.status(),
+            actix_web::http::StatusCode::BAD_REQUEST
+        );
+        let request = aw_test::TestRequest::delete()
+            .uri("/auth/users/admin")
+            .insert_header((actix_web::http::header::COOKIE, admin_cookie))
+            .to_request();
+        assert_eq!(
+            aw_test::call_service(&app, request).await.status(),
+            actix_web::http::StatusCode::BAD_REQUEST
+        );
     }
 }