add missing IDP required check for OTA profiles (#44644)

Found this missed TODO from some old story work.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Bug Fixes**
* Enhanced OTA enrollment profile validation to properly enforce
end-user authentication requirements when configured, now returning
appropriate error responses for requests missing required authentication
credentials.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

server/service/apple_mdm.go

@@ -6961,8 +6961,17 @@ func (svc *Service) GetOTAProfile(ctx context.Context, enrollSecret, idpUUID str
 		return nil, ctxerr.Wrap(ctx, err, "getting app config to get org name")
 	}
 
-	// TODO(IB): Validate that the IdpUUID should be populated based on the criteria for showing the SSO in the first place
-	// Should be added with the work of #30660 or afterwars.
+	requiresIDPUUID, err := shared_mdm.RequiresEnrollOTAAuthentication(ctx, svc.ds, enrollSecret, cfg.MDM.MacOSSetup.EnableEndUserAuthentication)
+	if err != nil {
+		return nil, ctxerr.Wrap(ctx, err, "checking if IDP UUID is required for OTA enrollment")
+	}
+	if requiresIDPUUID && idpUUID == "" {
+		return nil, ctxerr.Wrap(
+			ctx,
+			authz.ForbiddenWithInternal("required idp uuid to be set, but none found", nil, nil, nil),
+			"missing required idp uuid",
+		)
+	}
 
 	profBytes, err := apple_mdm.GenerateOTAEnrollmentProfileMobileconfig(cfg.OrgInfo.OrgName, cfg.MDMUrl(), enrollSecret, idpUUID)
 	if err != nil {

server/service/integration_mdm_profiles_test.go

@@ -6410,6 +6410,19 @@ func (s *integrationMDMTestSuite) TestOTAProfile() {
 		require.NotContains(t, string(b), "idp_uuid=")
 		require.Contains(t, string(b), cfg.OrgInfo.OrgName)
 	})
+
+	t.Run("returns 403 if no idp_uuid is set when required by config", func(t *testing.T) {
+		// update config to require idp_uuid
+		cfg.MDM.MacOSSetup.EnableEndUserAuthentication = true
+		err := s.ds.SaveAppConfig(ctx, cfg)
+		require.NoError(t, err)
+		t.Cleanup(func() {
+			cfg.MDM.MacOSSetup.EnableEndUserAuthentication = false
+			err := s.ds.SaveAppConfig(ctx, cfg)
+			require.NoError(t, err)
+		})
+		s.Do("GET", "/api/latest/fleet/enrollment_profiles/ota", &getOTAProfileRequest{}, http.StatusForbidden, "enroll_secret", globalEnrollSec)
+	})
 }
 
 // TestAppleDDMSecretVariablesUpload tests uploading DDM profiles with secrets via the /configuration_profiles endpoint