Are CA-signed certificates necessary for SAML security?

In the context of SAML (Security Assertion Markup Language) integrations, self-signed certificates are typically sufficient and secure, as SAML does not rely on the traditional Certificate Authority (CA) trust model used in HTTPS/TLS. Unlike web communications that require CA validation to establish trust, SAML certificates are used for cryptographic signing and verification directly between an Identity Provider (IdP) and a Service Provider (SP). This approach ensures that assertions are genuinely from the IdP and have not been altered, with trust established directly between the parties through the exchange of public certificates. While CA-signed certificates can be useful in certain situations, such as when organizational policies require them or for simplifying certificate management, they are not necessary for most SAML use cases. Self-signed certificates are widely used and accepted for SAML, with CA-signed certificates primarily mandated by internal security policies or regulatory requirements rather than by the SAML specification itself.