Password-based Authentication (Client Secret)
This is the simplest form of authentication for service principals. When you create a service principal in Azure Active Directory (AAD), you have the option to generate a password or secret that will be used for authentication.
Steps to configure password-based authentication:
- Sign in to the Azure portal and navigate to Azure Active Directory.
- Go to ‘App registrations’ and select the application associated with the service principal or create a new registration.
- In the application panel, click on ‘Certificates & secrets’.
- Under ‘Client secrets’, click on ‘New client secret’.
- Provide a description for the client secret, choose an expiration period, and then click ‘Add’.
- Once the client secret is created, note the value generated as it won’t be displayed again.
Example:
az ad sp create-for-rbac –name {Service-Principal-Name}
This command creates a new service principal with a client secret and assigns it a default role.
Certificate-based Authentication
For environments requiring higher security standards, certificate-based authentication is recommended. Certificates are considered more secure because they are cryptographically signed by a trusted authority and are more difficult to compromise than a password.
Steps to configure certificate-based authentication:
- Generate a certificate (self-signed or issued by a Certificate Authority).
- Sign in to the Azure portal.
- Navigate to Azure Active Directory and select ‘App registrations’.
- Choose the application tied to the service principal.
- In the application panel, go to ‘Certificates & secrets’.
- Click on ‘Upload certificate’ and select the certificate file to upload.
- Once the certificate is uploaded, Azure AD will use it for authentication purposes.
Example:
$cert = New-SelfSignedCertificate -Subject “CN=ServicePrincipalName” -CertStoreLocation “Cert:\CurrentUser\My” -KeyExportPolicy Exportable -KeySpec Signature
New-AzADServicePrincipal -DisplayName ServicePrincipalName -CertValue $cert.RawData
These commands create a new self-signed certificate and then use it to create a new service principal.
Comparison of Authentication Methods
Authentication Method | Level of Security | Expiry | Rotation Strategy | Use Case |
---|---|---|---|---|
Password (Client Secret) | Lower | Yes, based on the chosen period | Manual update of client secrets | Suitable for environments with a less strict security requirement |
Certificate | Higher | Yes, based on the certificate validity period | Requires certificate renewal and update in Azure AD | Recommended for production environments and where automated processes require higher security |
Securing Service Principal Authentication
Regardless of the authentication method chosen, the following best practices help to ensure that your service principals remain secure:
- Rotate credentials regularly to limit the exposure window of a potential compromised credential.
- Use Azure Key Vault to securely store and manage client secrets and certificates.
- Limit the permissions granted to a service principal to only those that are necessary (principle of least privilege).
- Monitor the use of service principals with Azure AD audit logs.
By understanding the available methods and following the recommended steps and best practices, you can configure a secure authentication method for your service principal, thereby securing application access to Azure resources while complying with security policies and standards.
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