Are CA-signed certificates necessary for SAML security?

!!TL;DR SAML doesn’t depend on the traditional CA trust model. Self-signed certificates are normal and secure, unless your organization has a specific compliance requirement.!!

When setting up a SAML integration, one of the most common questions we hear is: “Do I need a trusted CA-signed certificate for my SAML signatures?”

It’s a great question, because digital certificates and certificate authorities (CAs) are usually associated with secure communication on the web (think HTTPS). But in the world of SAML, the answer is a little different.

What’s a CA-signed certificate?

A CA-signed certificate is a digital certificate that’s been issued and validated by a Certificate Authority (CA); a trusted third party like DigiCert, GlobalSign, or Let’s Encrypt.

On the web, CAs play a critical role: your browser trusts them, which is why you can be confident that https://example.com really is the site it claims to be.

But in SAML, you don’t need that global trust model.

What role do certificates play in SAML?

Certificates in SAML are not about proving identity to the outside world (like with HTTPS). Instead, they are used for cryptographic signing and verification between the Identity Provider (IdP) and the Service Provider (SP).

• The IdP signs SAML assertions with its private key.
• The SP validates those assertions using the IdP’s public certificate.

This ensures two things:

1. The assertion really came from the IdP.
2. The contents weren’t altered in transit.

That’s all that’s needed for SAML to work securely.

Why a CA-signed certificate usually isn’t needed

Unlike HTTPS/TLS, where your browser needs to trust a certificate chain anchored by a known CA, SAML doesn’t depend on that global trust model. Instead, it uses explicit trust established directly between the two parties:

• The IdP generates its certificate and shares the public key (part of the certificate) with the SP, often through a separate channel like email or a configuration portal.
• The SP installs and trusts only that certificate.
• From then on, any assertion signed with the corresponding private key will be accepted.

Because trust is established in this one-to-one way, there’s no requirement for a third-party CA. That’s why self-signed certificates are perfectly acceptable, and in fact, what most organizations use for SAML federation.

When might a CA-signed certificate be useful?

There are a few edge cases where a CA-signed certificate can still be helpful:

• Enterprise policy requirements: Some organizations have internal security or compliance policies that mandate CA-signed certificates for all cryptographic material, even when not technically required.
• Certificate lifecycle management: Using a CA may simplify certificate rotation, renewal, or revocation if the company already has established tooling around PKI.
• Audit and compliance assurance: In regulated industries, auditors may feel more comfortable seeing CA-backed certificates even if they don’t change the security posture in SAML.

The bottom line

For most SAML use cases, a self-signed certificate provides the same security guarantees as a CA-signed one. The key factor is whether both the IdP and SP are configured to trust the same certificate.

• Self-signed certificates are secure and standard in SAML.
• CA-signed certificates are optional and usually only required by organizational policy, not by the SAML specification itself.

If you’re setting up a SAML connection and wondering whether you need to pay for or request a CA-signed certificate, the answer is almost always: “No, you’re fine with a self-signed certificate.”