diff --git a/.changeset/admin-as-app-normalize-store.md b/.changeset/admin-as-app-normalize-store.md
new file mode 100644
index 00000000000..0a9e31ded4a
--- /dev/null
+++ b/.changeset/admin-as-app-normalize-store.md
@@ -0,0 +1,5 @@
+---
+'@shopify/cli-kit': patch
+---
+
+Normalize and validate the store domain in `ensureAuthenticatedAdminAsApp` before sending the app's client secret.
diff --git a/packages/app/src/cli/services/app-security-commands.test.ts b/packages/app/src/cli/services/app-security-commands.test.ts
index 3412894b8a4..fe5e00a5f34 100644
--- a/packages/app/src/cli/services/app-security-commands.test.ts
+++ b/packages/app/src/cli/services/app-security-commands.test.ts
@@ -508,6 +508,8 @@ describe('formatAppSecurityCommand', () => {
 
   test.skipIf(process.platform !== 'win32')(
     'the PowerShell record command reads a findings file without a byte order mark as UTF-8 in Windows PowerShell 5.1',
+    // Native PowerShell startup needs its own allowance on shared Windows runners.
+    {timeout: 30000},
     async () => {
       await inTemporaryDirectory(async (directory) => {
         const findingsPath = joinPath(directory, 'findings.json')
@@ -531,9 +533,10 @@ describe('formatAppSecurityCommand', () => {
         const result = spawnSync(
           'powershell.exe',
           ['-NoProfile', '-NonInteractive', '-EncodedCommand', Buffer.from(script, 'utf16le').toString('base64')],
-          {encoding: 'utf8', windowsHide: true},
+          {encoding: 'utf8', windowsHide: true, timeout: 25000},
         )
 
+        expect(result.error).toBeUndefined()
         expect(result.status, result.stderr).toBe(0)
         expect(JSON.parse(await readFile(receivedPath))).toStrictEqual({file: 'app/café.ts'})
       })
diff --git a/packages/cli-kit/src/public/node/session.test.ts b/packages/cli-kit/src/public/node/session.test.ts
index 5236d53a49d..5aa72a0a4e2 100644
--- a/packages/cli-kit/src/public/node/session.test.ts
+++ b/packages/cli-kit/src/public/node/session.test.ts
@@ -512,4 +512,53 @@ describe('ensureAuthenticatedAdminAsApp', () => {
     // Then
     await expect(got).rejects.toThrow('Failed to get access token for app client123 on store mystore.myshopify.com')
   })
+
+  test('normalizes the store before sending the client secret', async () => {
+    // Given
+    vi.mocked(shopifyFetch).mockResolvedValueOnce({
+      status: 200,
+      text: async () => JSON.stringify({access_token: 'app_access_token'}),
+    } as any)
+
+    // When
+    const got = await ensureAuthenticatedAdminAsApp('mystore', 'client123', 'secret456')
+
+    // Then
+    expect(shopifyFetch).toHaveBeenCalledWith(
+      'https://mystore.myshopify.com/admin/oauth/access_token',
+      expect.anything(),
+      'slow-request',
+    )
+    expect(got).toEqual({token: 'app_access_token', storeFqdn: 'mystore.myshopify.com'})
+  })
+
+  test('only sends the client secret to a Shopify store domain', async () => {
+    // Given
+    vi.mocked(shopifyFetch).mockResolvedValueOnce({
+      status: 200,
+      text: async () => JSON.stringify({access_token: 'app_access_token'}),
+    } as any)
+
+    // When
+    await ensureAuthenticatedAdminAsApp('evil.attacker.test', 'client123', 'secret456')
+
+    // Then
+    expect(shopifyFetch).toHaveBeenCalledWith(
+      'https://evil.attacker.test.myshopify.com/admin/oauth/access_token',
+      expect.anything(),
+      'slow-request',
+    )
+  })
+
+  test.each(['evil.attacker.test:8443', 'mystore.myshopify.com:8443', 'user@mystore.myshopify.com'])(
+    'rejects %s without sending the client secret',
+    async (store) => {
+      // When
+      const got = ensureAuthenticatedAdminAsApp(store, 'client123', 'secret456')
+
+      // Then
+      await expect(got).rejects.toThrow(`Invalid store value: ${store}`)
+      expect(shopifyFetch).not.toHaveBeenCalled()
+    },
+  )
 })
diff --git a/packages/cli-kit/src/public/node/session.ts b/packages/cli-kit/src/public/node/session.ts
index 5ec9a3288b0..ef93c864a6e 100644
--- a/packages/cli-kit/src/public/node/session.ts
+++ b/packages/cli-kit/src/public/node/session.ts
@@ -2,6 +2,7 @@ import {shopifyFetch} from './http.js'
 import {nonRandomUUID} from './crypto.js'
 import {getAppAutomationToken} from './environment.js'
 import {AbortError, BugError} from './error.js'
+import {normalizeStoreFqdn} from './context/fqdn.js'
 import {outputContent, outputToken, outputDebug} from './output.js'
 import * as sessionStore from '../../private/node/session/store.js'
 import {automationTokenVariable} from '../../private/node/session/automation-token.js'
@@ -391,7 +392,8 @@ export function logout(): Promise<void> {
  *
  * See `ensureAuthenticatedAdmin` for access on behalf of a user.
  *
- * @param storeFqdn - Store fqdn to request auth for.
+ * @param storeFqdn - Store handle or domain, normalized with `normalizeStoreFqdn`. Unsupported URL components are
+ * rejected before the client secret is sent.
  * @param clientId - Client ID of the app.
  * @param clientSecret - Client secret of the app.
  * @returns The access token for the Admin API.
@@ -401,13 +403,14 @@ export async function ensureAuthenticatedAdminAsApp(
   clientId: string,
   clientSecret: string,
 ): Promise<AdminSession> {
+  const normalizedStoreFqdn = normalizeStoreFqdn(storeFqdn)
   const bodyData = {
     client_id: clientId,
     client_secret: clientSecret,
     grant_type: 'client_credentials',
   }
   const tokenResponse = await shopifyFetch(
-    `https://${storeFqdn}/admin/oauth/access_token`,
+    `https://${normalizedStoreFqdn}/admin/oauth/access_token`,
     {
       method: 'POST',
       headers: {
@@ -424,17 +427,17 @@ export async function ensureAuthenticatedAdminAsApp(
     if (body.includes('app_not_installed')) {
       throw new AbortError(
         outputContent`App is not installed on ${outputToken.green(
-          storeFqdn,
+          normalizedStoreFqdn,
         )}. Try running ${outputToken.genericShellCommand(`shopify app dev`)} to connect your app to the shop.`,
       )
     }
     throw new AbortError(
-      `Failed to get access token for app ${clientId} on store ${storeFqdn}: ${tokenResponse.statusText}`,
+      `Failed to get access token for app ${clientId} on store ${normalizedStoreFqdn}: ${tokenResponse.statusText}`,
     )
   }
   try {
     const tokenJson = JSON.parse(body) as {access_token: string}
-    return {token: tokenJson.access_token, storeFqdn}
+    return {token: tokenJson.access_token, storeFqdn: normalizedStoreFqdn}
   } catch (error) {
     if (error instanceof SyntaxError) {
       throw new AbortError(