diff --git a/docs/5-add-identity.md b/docs/5-add-identity.md
index bf3d33206..095021efe 100644
--- a/docs/5-add-identity.md
+++ b/docs/5-add-identity.md
@@ -83,6 +83,7 @@ We'll create two GitHub apps: one for testing locally and another for production
 AZURE_AD_CLIENT_ID=
 AZURE_AD_CLIENT_SECRET=
 AZURE_AD_TENANT_ID=
+AZURE_AD_ALLOWED_PRINCIPALS=
 ```
 
 ## Configure an admin user
diff --git a/docs/7-environment-variables.md b/docs/7-environment-variables.md
index 0accbe5b8..7da761892 100644
--- a/docs/7-environment-variables.md
+++ b/docs/7-environment-variables.md
@@ -17,6 +17,7 @@ Below are the required environment variables, to be added to the Azure Portal or
 | `AZURE_AD_CLIENT_ID`                                                                      |                                                | The client id specific to the application                                                                                                 |
 | `AZURE_AD_CLIENT_SECRET`                                                                  |                                                | The client secret specific to the application                                                                                             |
 | `AZURE_AD_TENANT_ID`                                                                      |                                                | The organisation Tenant ID                                                                                                                |
+| `AZURE_AD_ALLOWED_PRINCIPALS`                                                             |                                                | Comma separated list of Object IDs for users/groups that are allowed to log in. **All authenticated users are allowed by default**        |
 | `ADMIN_EMAIL_ADDRESS`                                                                     |                                                | Comma separated list of email addresses of the admin users ID                                                                             |
 | **Azure Cognitive Search is optional. This is only required for chat over file feature.** |
 | `AZURE_SEARCH_API_KEY`                                                                    |                                                | API Key of Azure Cognitive search                                                                                                         |
diff --git a/src/features/auth/auth-api.ts b/src/features/auth/auth-api.ts
index 73fbc0cb6..e1f73b31c 100644
--- a/src/features/auth/auth-api.ts
+++ b/src/features/auth/auth-api.ts
@@ -8,7 +8,8 @@ import { hashValue } from "./helpers";
 const configureIdentityProvider = () => {
   const providers: Array<Provider> = [];
 
-  const adminEmails = process.env.ADMIN_EMAIL_ADDRESS?.split(",").map(email => email.toLowerCase().trim());
+  const adminEmails = process.env.ADMIN_EMAIL_ADDRESS?.split(",").map(email => email.toLowerCase().trim()).filter(email => email);
+  const azureAdAllowedPrincipals = process.env.AZURE_AD_ALLOWED_PRINCIPALS?.split(",").map(oid => oid.toLowerCase().trim()).filter(oid => oid);
 
   if (process.env.AUTH_GITHUB_ID && process.env.AUTH_GITHUB_SECRET) {
     providers.push(
@@ -18,7 +19,8 @@ const configureIdentityProvider = () => {
         async profile(profile) {
           const newProfile = {
             ...profile,
-            isAdmin: adminEmails?.includes(profile.email.toLowerCase())
+            isAdmin: adminEmails?.includes(profile.email.toLowerCase()),
+            isAllowed: true
           }
           return newProfile;
         }
@@ -36,13 +38,60 @@ const configureIdentityProvider = () => {
         clientId: process.env.AZURE_AD_CLIENT_ID!,
         clientSecret: process.env.AZURE_AD_CLIENT_SECRET!,
         tenantId: process.env.AZURE_AD_TENANT_ID!,
-        async profile(profile) {
-
+        authorization: {
+          params: {
+            // Add User.Read to reach the /me endpoint of Microsoft Graph
+            scope: 'email openid profile User.Read'
+          }
+        },
+        async profile(profile, tokens) {
+          let isAllowed = true
+          if (Array.isArray(azureAdAllowedPrincipals) && azureAdAllowedPrincipals.length > 0) {
+            try {
+              isAllowed = false
+              // POST https://graph.microsoft.com/v1.0/me/getMemberObjects
+              // It returns all IDs of principal objects which "me" is a member of (transitive)
+              // https://learn.microsoft.com/en-us/graph/api/directoryobject-getmemberobjects?view=graph-rest-1.0&tabs=http
+              const response = await fetch(
+                'https://graph.microsoft.com/v1.0/me/getMemberObjects',
+                {
+                  method: 'POST',
+                  headers: {
+                    Authorization: `Bearer ${tokens.access_token}`,
+                    'Content-Type': 'application/json'
+                  },
+                  body: '{"securityEnabledOnly":true}'
+                }
+              )
+              if (response.ok) {
+                const body = await response.json() as { value?: string[] }
+                const oids = body.value ?? []
+                if (profile.oid) {
+                  // Append the object ID of user principal "me"
+                  oids.push(profile.oid)
+                }
+                for (const principal of azureAdAllowedPrincipals) {
+                  if (oids.includes(principal)) {
+                    isAllowed = true
+                    break
+                  }
+                }
+              }
+              else {
+                const body = await response.text()
+                throw new Error(`Bad response from POST /me/getMemberObjects: ${response.status} ${response.statusText}: ${body}`)
+              }
+            }
+            catch (e) {
+              console.log(e)
+            }
+          }
           const newProfile = {
             ...profile,
             // throws error without this - unsure of the root cause (https://stackoverflow.com/questions/76244244/profile-id-is-missing-in-google-oauth-profile-response-nextauth)
             id: profile.sub,
-            isAdmin: adminEmails?.includes(profile.email.toLowerCase()) || adminEmails?.includes(profile.preferred_username.toLowerCase())
+            isAdmin: adminEmails?.includes(profile.email.toLowerCase()) || adminEmails?.includes(profile.preferred_username.toLowerCase()),
+            isAllowed
           }
           return newProfile;
         }
@@ -89,15 +138,18 @@ export const options: NextAuthOptions = {
   secret: process.env.NEXTAUTH_SECRET,
   providers: [...configureIdentityProvider()],
   callbacks: {
-    async jwt({token, user, account, profile, isNewUser, session}) {
+    async jwt({ token, user, account, profile, isNewUser, session }) {
       if (user?.isAdmin) {
-       token.isAdmin = user.isAdmin
+        token.isAdmin = user.isAdmin
       }
       return token
     },
-    async session({session, token, user }) {
+    async session({ session, token, user }) {
       session.user.isAdmin = token.isAdmin as string
       return session
+    },
+    async signIn({ user }) {
+      return user.isAllowed
     }
   },
   session: {
diff --git a/src/types/next-auth.d.ts b/src/types/next-auth.d.ts
index 1e44d8162..e970276be 100644
--- a/src/types/next-auth.d.ts
+++ b/src/types/next-auth.d.ts
@@ -12,6 +12,7 @@ declare module "next-auth" {
 
     interface User {
         isAdmin: string
+        isAllowed: boolean
     }
 
 }