Cis Azure Compute 2.3.11

Ensure 'App Service authentication' is set to 'Enabled'

Description

App Service authentication can prevent anonymous HTTP requests from reaching an app, or authenticate those with tokens before they reach the app. If an anonymous request is received from a browser, App Service will redirect to a login page. To handle the login process, a choice from a set of identity providers can be made, or a custom authentication mechanism can be implemented.

Rationale

By enabling authentication, every incoming HTTP request passes through it before being handled by the application code. It also handles authentication of users with the specified provider (Entra ID, Facebook, Google, Microsoft Account, and Twitter), validation, storage and refreshing of tokens, managing the authenticated sessions, and injecting identity information into request headers.

Impact

This is only required for apps that require authentication. Enabling it on a site like a marketing or support website will prevent unauthenticated access, which would be undesirable.

Adding an authentication requirement will increase costs and require additional security components to facilitate the authentication.

Audit Procedure

Using Azure Portal

1. Go to App Services or Function App.
2. Click the name of a function app.
3. Under Settings, click Authentication.
4. Ensure that App Service authentication is set to Enabled.
5. Repeat steps 1-4 for each function app.

Using Azure CLI

Run the following command to list function apps:

az functionapp list

For each function app, run the following command to get the authentication setting:

For v1 auth commands:

az webapp auth show --resource-group <resource-group-name> --name <function-app-name> --query enabled

For v2 auth commands:

az webapp auth show --resource-group <resource-group-name> --name <function-app-name> --query properties.platform.enabled

Ensure that true is returned.

Expected Result

App Service authentication should be enabled (return true).

Remediation

Using Azure Portal

1. Go to App Services or Function App.
2. Click the name of a function app.
3. Under Settings, click Authentication.
4. If an identity provider is not configured:
   1. Click Add identity provider.
   2. Provide appropriate configuration for an identity provider and click Add.
5. If App Service authentication is set to Disabled:
   1. Click Enable authentication.
6. Repeat steps 1-5 for each function app requiring remediation.

Using Azure CLI

For each function app requiring remediation, run the following command to enable authentication:

az webapp auth update --resource-group <resource-group-name> --name <function-app-name> --enabled true

Note: In order to access App Service authentication settings for an app using the Microsoft API, the Website Contributor permission at the subscription level is required. A custom role can be created instead of Website Contributor to provide more specific permissions and maintain the principle of least privileged access.

Default Value

By default, App Service authentication is set to Disabled.

Additional Information

You're not required to use App Service for authentication and authorization. Many web frameworks come with security features built in, and you can use them if you like. If you need more flexibility than App Service provides, you can also write your own utilities. Secure authentication and authorization require a deep understanding of security, including federation, encryption, JSON Web Token (JWT) management, grant types, and so on.

References

1. https://learn.microsoft.com/en-us/azure/app-service/overview-authentication-authorization
2. https://learn.microsoft.com/en-us/azure/role-based-access-control/built-in-roles#website-contributor
3. https://learn.microsoft.com/en-us/security/benchmark/azure/mcsb-privileged-access#pa-3-manage-lifecycle-of-identities-and-entitlements
4. https://learn.microsoft.com/en-us/security/benchmark/azure/mcsb-governance-strategy#gs-6-define-and-implement-identity-and-privileged-access-strategy
5. https://learn.microsoft.com/en-us/cli/azure/webapp/auth

Profile

Level 2 | Automated