diff --git a/packages/mosaic/src/cli.ts b/packages/mosaic/src/cli.ts
index 2a0a579..5c1a07a 100644
--- a/packages/mosaic/src/cli.ts
+++ b/packages/mosaic/src/cli.ts
@@ -14,6 +14,7 @@ import { registerConfigCommand } from './commands/config.js';
 import { registerMissionCommand } from './commands/mission.js';
 // prdy is registered via launch.ts
 import { registerLaunchCommands } from './commands/launch.js';
+import { registerAuthCommand } from './commands/auth.js';
 import { registerGatewayCommand } from './commands/gateway.js';
 import {
   backgroundUpdateCheck,
@@ -328,6 +329,10 @@ sessionsCmd
     }
   });
 
+// ─── auth ────────────────────────────────────────────────────────────────
+
+registerAuthCommand(program);
+
 // ─── gateway ──────────────────────────────────────────────────────────
 
 registerGatewayCommand(program);
diff --git a/packages/mosaic/src/commands/auth.spec.ts b/packages/mosaic/src/commands/auth.spec.ts
new file mode 100644
index 0000000..8c5e425
--- /dev/null
+++ b/packages/mosaic/src/commands/auth.spec.ts
@@ -0,0 +1,114 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { Command } from 'commander';
+
+// ─── Mocks ──────────────────────────────────────────────────────────────────
+// These mocks prevent any real disk/network access during tests.
+
+vi.mock('./gateway/login.js', () => ({
+  getGatewayUrl: vi.fn().mockReturnValue('http://localhost:14242'),
+}));
+
+vi.mock('./gateway/token-ops.js', () => ({
+  requireSession: vi.fn().mockResolvedValue('better-auth.session_token=test'),
+}));
+
+// Global fetch is never called in smoke tests (no actions invoked).
+
+import { registerAuthCommand } from './auth.js';
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+function buildTestProgram(): Command {
+  const program = new Command('mosaic').exitOverride();
+  registerAuthCommand(program);
+  return program;
+}
+
+function findCommand(program: Command, ...path: string[]): Command | undefined {
+  let current: Command = program;
+  for (const name of path) {
+    const found = current.commands.find((c) => c.name() === name);
+    if (!found) return undefined;
+    current = found;
+  }
+  return current;
+}
+
+// ─── Tests ───────────────────────────────────────────────────────────────────
+
+describe('registerAuthCommand', () => {
+  let program: Command;
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    program = buildTestProgram();
+  });
+
+  it('registers the top-level auth command', () => {
+    const authCmd = findCommand(program, 'auth');
+    expect(authCmd).toBeDefined();
+    expect(authCmd?.name()).toBe('auth');
+  });
+
+  describe('auth users', () => {
+    it('registers the users subcommand', () => {
+      const usersCmd = findCommand(program, 'auth', 'users');
+      expect(usersCmd).toBeDefined();
+    });
+
+    it('registers users list with --limit flag', () => {
+      const listCmd = findCommand(program, 'auth', 'users', 'list');
+      expect(listCmd).toBeDefined();
+      const limitOpt = listCmd?.options.find((o) => o.long === '--limit');
+      expect(limitOpt).toBeDefined();
+    });
+
+    it('registers users create', () => {
+      const createCmd = findCommand(program, 'auth', 'users', 'create');
+      expect(createCmd).toBeDefined();
+    });
+
+    it('registers users delete with --yes flag', () => {
+      const deleteCmd = findCommand(program, 'auth', 'users', 'delete');
+      expect(deleteCmd).toBeDefined();
+      const yesOpt = deleteCmd?.options.find((o) => o.long === '--yes');
+      expect(yesOpt).toBeDefined();
+    });
+  });
+
+  describe('auth sso', () => {
+    it('registers the sso subcommand', () => {
+      const ssoCmd = findCommand(program, 'auth', 'sso');
+      expect(ssoCmd).toBeDefined();
+    });
+
+    it('registers sso list', () => {
+      const listCmd = findCommand(program, 'auth', 'sso', 'list');
+      expect(listCmd).toBeDefined();
+    });
+
+    it('registers sso test', () => {
+      const testCmd = findCommand(program, 'auth', 'sso', 'test');
+      expect(testCmd).toBeDefined();
+    });
+  });
+
+  describe('auth sessions', () => {
+    it('registers the sessions subcommand', () => {
+      const sessCmd = findCommand(program, 'auth', 'sessions');
+      expect(sessCmd).toBeDefined();
+    });
+
+    it('registers sessions list', () => {
+      const listCmd = findCommand(program, 'auth', 'sessions', 'list');
+      expect(listCmd).toBeDefined();
+    });
+  });
+
+  it('all top-level auth subcommand names are correct', () => {
+    const authCmd = findCommand(program, 'auth');
+    expect(authCmd).toBeDefined();
+    const names = authCmd!.commands.map((c) => c.name()).sort();
+    expect(names).toEqual(['sessions', 'sso', 'users']);
+  });
+});
diff --git a/packages/mosaic/src/commands/auth.ts b/packages/mosaic/src/commands/auth.ts
new file mode 100644
index 0000000..6d190b7
--- /dev/null
+++ b/packages/mosaic/src/commands/auth.ts
@@ -0,0 +1,331 @@
+import type { Command } from 'commander';
+import { getGatewayUrl } from './gateway/login.js';
+import { requireSession } from './gateway/token-ops.js';
+
+// ─── Types ───────────────────────────────────────────────────────────────────
+
+interface UserDto {
+  id: string;
+  name: string;
+  email: string;
+  role: string;
+  banned: boolean;
+  banReason: string | null;
+  createdAt: string;
+  updatedAt: string;
+}
+
+interface UserListDto {
+  users: UserDto[];
+  total: number;
+}
+
+// ─── HTTP helpers ────────────────────────────────────────────────────────────
+
+async function adminGet<T>(gatewayUrl: string, cookie: string, path: string): Promise<T> {
+  let res: Response;
+  try {
+    res = await fetch(`${gatewayUrl}${path}`, {
+      headers: { Cookie: cookie, Origin: gatewayUrl },
+    });
+  } catch (err) {
+    console.error(
+      `Could not reach gateway at ${gatewayUrl}: ${err instanceof Error ? err.message : String(err)}`,
+    );
+    process.exit(1);
+  }
+
+  if (res.status === 401 || res.status === 403) {
+    console.error(`Session rejected by the gateway (${res.status.toString()}).`);
+    console.error('Run: mosaic gateway login');
+    process.exit(2);
+  }
+
+  if (!res.ok) {
+    const body = await res.text().catch(() => '');
+    console.error(`Gateway returned error (${res.status.toString()}): ${body.slice(0, 200)}`);
+    process.exit(3);
+  }
+
+  return res.json() as Promise<T>;
+}
+
+async function adminPost<T>(
+  gatewayUrl: string,
+  cookie: string,
+  path: string,
+  body: unknown,
+): Promise<T> {
+  let res: Response;
+  try {
+    res = await fetch(`${gatewayUrl}${path}`, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        Cookie: cookie,
+        Origin: gatewayUrl,
+      },
+      body: JSON.stringify(body),
+    });
+  } catch (err) {
+    console.error(
+      `Could not reach gateway at ${gatewayUrl}: ${err instanceof Error ? err.message : String(err)}`,
+    );
+    process.exit(1);
+  }
+
+  if (res.status === 401 || res.status === 403) {
+    console.error(`Session rejected by the gateway (${res.status.toString()}).`);
+    console.error('Run: mosaic gateway login');
+    process.exit(2);
+  }
+
+  if (!res.ok) {
+    const body = await res.text().catch(() => '');
+    console.error(`Gateway returned error (${res.status.toString()}): ${body.slice(0, 200)}`);
+    process.exit(3);
+  }
+
+  return res.json() as Promise<T>;
+}
+
+async function adminDelete(gatewayUrl: string, cookie: string, path: string): Promise<void> {
+  let res: Response;
+  try {
+    res = await fetch(`${gatewayUrl}${path}`, {
+      method: 'DELETE',
+      headers: { Cookie: cookie, Origin: gatewayUrl },
+    });
+  } catch (err) {
+    console.error(
+      `Could not reach gateway at ${gatewayUrl}: ${err instanceof Error ? err.message : String(err)}`,
+    );
+    process.exit(1);
+  }
+
+  if (res.status === 401 || res.status === 403) {
+    console.error(`Session rejected by the gateway (${res.status.toString()}).`);
+    console.error('Run: mosaic gateway login');
+    process.exit(2);
+  }
+
+  if (!res.ok && res.status !== 204) {
+    const body = await res.text().catch(() => '');
+    console.error(`Gateway returned error (${res.status.toString()}): ${body.slice(0, 200)}`);
+    process.exit(3);
+  }
+}
+
+// ─── Formatters ──────────────────────────────────────────────────────────────
+
+function printUser(u: UserDto): void {
+  console.log(`  ID:        ${u.id}`);
+  console.log(`  Name:      ${u.name}`);
+  console.log(`  Email:     ${u.email}`);
+  console.log(`  Role:      ${u.role}`);
+  console.log(`  Banned:    ${u.banned ? `yes (${u.banReason ?? 'no reason'})` : 'no'}`);
+  console.log(`  Created:   ${new Date(u.createdAt).toLocaleString()}`);
+  console.log('');
+}
+
+// ─── Register function ───────────────────────────────────────────────────────
+
+/**
+ * Register `mosaic auth` subcommands on an existing Commander program.
+ *
+ * Location rationale: placed in packages/mosaic rather than packages/auth because
+ * the CLI needs session helpers (loadSession, validateSession, requireSession)
+ * and gateway URL resolution (getGatewayUrl) that live in packages/mosaic.
+ * Keeping packages/auth as a pure server-side library avoids adding commander
+ * and CLI tooling as dependencies there.
+ */
+export function registerAuthCommand(parent: Command): void {
+  const auth = parent
+    .command('auth')
+    .description('Manage gateway authentication, users, SSO providers, and sessions')
+    .configureHelp({ sortSubcommands: true })
+    .action(() => {
+      auth.outputHelp();
+    });
+
+  // ─── users ──────────────────────────────────────────────────────────────
+
+  const users = auth
+    .command('users')
+    .description('Manage gateway users')
+    .configureHelp({ sortSubcommands: true })
+    .action(() => {
+      users.outputHelp();
+    });
+
+  users
+    .command('list')
+    .description('List all users on the gateway')
+    .option('-g, --gateway <url>', 'Gateway URL')
+    .option('-l, --limit <n>', 'Maximum number of users to display', '100')
+    .action(async (opts: { gateway?: string; limit: string }) => {
+      const url = getGatewayUrl(opts.gateway);
+      const cookie = await requireSession(url);
+      const limit = parseInt(opts.limit, 10);
+
+      const result = await adminGet<UserListDto>(url, cookie, '/api/admin/users');
+
+      const subset = result.users.slice(0, limit);
+      if (subset.length === 0) {
+        console.log('No users found.');
+        return;
+      }
+
+      console.log(`Users (${subset.length.toString()} of ${result.total.toString()}):\n`);
+      for (const u of subset) {
+        printUser(u);
+      }
+    });
+
+  users
+    .command('create')
+    .description('Create a new gateway user (interactive prompts)')
+    .option('-g, --gateway <url>', 'Gateway URL')
+    .action(async (opts: { gateway?: string }) => {
+      const url = getGatewayUrl(opts.gateway);
+      const cookie = await requireSession(url);
+
+      const {
+        text,
+        password: clackPassword,
+        select,
+        intro,
+        outro,
+        isCancel,
+      } = await import('@clack/prompts');
+
+      intro('Create a new Mosaic gateway user');
+
+      const name = await text({ message: 'Full name:', placeholder: 'Jane Doe' });
+      if (isCancel(name)) {
+        outro('Cancelled.');
+        process.exit(0);
+      }
+
+      const email = await text({ message: 'Email:', placeholder: 'jane@example.com' });
+      if (isCancel(email)) {
+        outro('Cancelled.');
+        process.exit(0);
+      }
+
+      const pw = await clackPassword({ message: 'Password:' });
+      if (isCancel(pw)) {
+        outro('Cancelled.');
+        process.exit(0);
+      }
+
+      const role = await select({
+        message: 'Role:',
+        options: [
+          { value: 'member', label: 'member' },
+          { value: 'admin', label: 'admin' },
+        ],
+      });
+      if (isCancel(role)) {
+        outro('Cancelled.');
+        process.exit(0);
+      }
+
+      const created = await adminPost<UserDto>(url, cookie, '/api/admin/users', {
+        name: name as string,
+        email: email as string,
+        password: pw as string,
+        role: role as string,
+      });
+
+      outro(`User created: ${created.email} (${created.id})`);
+    });
+
+  users
+    .command('delete <id>')
+    .description('Delete a gateway user by ID')
+    .option('-g, --gateway <url>', 'Gateway URL')
+    .option('-y, --yes', 'Skip confirmation prompt')
+    .action(async (id: string, opts: { gateway?: string; yes?: boolean }) => {
+      const url = getGatewayUrl(opts.gateway);
+      const cookie = await requireSession(url);
+
+      if (!opts.yes) {
+        const { confirm, isCancel } = await import('@clack/prompts');
+        const confirmed = await confirm({
+          message: `Delete user ${id}? This cannot be undone.`,
+        });
+        if (isCancel(confirmed) || !confirmed) {
+          console.log('Aborted.');
+          process.exit(0);
+        }
+      }
+
+      await adminDelete(url, cookie, `/api/admin/users/${id}`);
+      console.log(`User ${id} deleted.`);
+    });
+
+  // ─── sso ────────────────────────────────────────────────────────────────
+
+  const sso = auth
+    .command('sso')
+    .description('Manage SSO provider configuration')
+    .configureHelp({ sortSubcommands: true })
+    .action(() => {
+      sso.outputHelp();
+    });
+
+  sso
+    .command('list')
+    .description('List configured SSO providers (reads gateway discovery endpoint if available)')
+    .option('-g, --gateway <url>', 'Gateway URL')
+    .action(async (opts: { gateway?: string }) => {
+      // The admin SSO discovery endpoint is not yet wired server-side.
+      // The buildSsoDiscovery helper in @mosaicstack/auth reads env-vars on the
+      // server; there is no GET /api/admin/sso endpoint in apps/gateway/src/admin/.
+      // Stub until a gateway admin route is wired.
+      console.log(
+        'not yet wired — admin endpoint missing (GET /api/admin/sso not implemented server-side)',
+      );
+      console.log(
+        'Hint: SSO providers are configured via environment variables (AUTHENTIK_*, WORKOS_*, KEYCLOAK_*).',
+      );
+      // Suppress unused variable warning
+      void opts;
+    });
+
+  sso
+    .command('test <provider>')
+    .description('Smoke-test a configured SSO provider')
+    .option('-g, --gateway <url>', 'Gateway URL')
+    .action(async (provider: string, opts: { gateway?: string }) => {
+      // No server-side SSO smoke-test endpoint exists yet.
+      console.log(
+        `not yet wired — admin endpoint missing (POST /api/admin/sso/${provider}/test not implemented server-side)`,
+      );
+      void opts;
+    });
+
+  // ─── sessions ────────────────────────────────────────────────────────────
+
+  const authSessions = auth
+    .command('sessions')
+    .description('Manage BetterAuth user sessions stored on the gateway')
+    .configureHelp({ sortSubcommands: true })
+    .action(() => {
+      authSessions.outputHelp();
+    });
+
+  authSessions
+    .command('list')
+    .description('List active user sessions')
+    .option('-g, --gateway <url>', 'Gateway URL')
+    .action(async (opts: { gateway?: string }) => {
+      // No GET /api/admin/auth-sessions endpoint exists in apps/gateway/src/admin/.
+      // Stub until a gateway admin route is wired.
+      console.log(
+        'not yet wired — admin endpoint missing (GET /api/admin/auth-sessions not implemented server-side)',
+      );
+      void opts;
+    });
+}