What is URI SAN (Uniform Resource Identifier Subject Alternative Name)?

URI SAN (Uniform Resource Identifier Subject Alternative Name) is a specialized type of Subject Alternative Name extension that identifies resources by their complete web address rather than just domain names. This allows SSL certificates to secure specific web resources, services, or applications rather than just traditional websites, providing more granular security coverage.

URI SAN Structure and Usage

URI SANs differ from standard DNS-based SANs in several important ways:

Complete Resource Identification: Includes protocol, domain, path, and query parameters
Service-Specific Security: Can secure particular web services or API endpoints
Application Integration: Useful for securing specific application resources
Protocol Flexibility: Supports various URI schemes beyond HTTP/HTTPS
Resource Validation: Enables certificate validation for non-traditional web resources

Applications and Benefits

URI SANs are particularly valuable in modern application architectures including microservices, API gateways, and specialized web applications that need to secure specific resource paths rather than entire domains. They enable more precise certificate scope control and can help implement fine-grained security policies. However, URI SANs require careful planning during certificate design and may have limited support in some older systems or applications that expect traditional domain-based certificates.