I'm migrating my application from Spring Boot 3.3.6 to 3.4.1.
I have a certification file used for SAML authentication. It's like
And I set it as

spring.security.saml2:
  relyingparty:
    registration:
      azuread: # registration id
        entity-id: ArchitecturePoC # entity id of project, need to be registered to Azure AD in advance
        assertingparty:
          verification:
            credentials:
              - certificate-location: "classpath:ArchitecturePoC.cer" 

It worked fine on spring boot 3.3.6, but when I upgraded to 3.4.1, the certification file cannot be recognized.

Caused by: java.lang.IllegalStateException: Missing certificates or unrecognized format
    at org.springframework.util.Assert.state(Assert.java:79)
    at org.springframework.boot.ssl.pem.PemCertificateParser.parse(PemCertificateParser.java:64)
    at org.springframework.boot.ssl.pem.PemContent.getCertificates(PemContent.java:64)
    at org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyRegistrationConfiguration.readCertificate(Saml2RelyingPartyRegistrationConfiguration.java:192)
    ... 97 common frames omitted

It seems to be the changes in Saml2RelyingPartyRegistrationConfiguration#readCertificate, in 3.3.x, it's like

    private X509Certificate readCertificate(Resource location) {
        Assert.state(location != null, "No certificate location specified");
        Assert.state(location.exists(), () -> "Certificate  location '" + location + "' does not exist");
        try (InputStream inputStream = location.getInputStream()) {
            return (X509Certificate) CertificateFactory.getInstance("X.509").generateCertificate(inputStream);
        }
        catch (Exception ex) {
            throw new IllegalArgumentException(ex);
        }
    }

in 3.4.x, it's

    private X509Certificate readCertificate(Resource location) {
        Assert.state(location != null, "No certificate location specified");
        Assert.state(location.exists(), () -> "Certificate  location '" + location + "' does not exist");
        try (InputStream inputStream = location.getInputStream()) {
            PemContent pemContent = PemContent.load(inputStream);
            List<X509Certificate> certificates = pemContent.getCertificates();
            return certificates.get(0);
        }
        catch (Exception ex) {
            throw new IllegalArgumentException(ex);
        }
    }

I cannot see the necessity of forcing apps to use pem files starts with BEGIN CERTIFICATE, and it makes no sense to stop supporting certifications which are not pem format.