config/src/main/java/org/springframework/security/config/annotation/web/configurers/X509Configurer.java
public X509Configurer<H> subjectPrincipalRegex(String subjectPrincipalRegex) {
		SubjectDnX509PrincipalExtractor principalExtractor = new SubjectDnX509PrincipalExtractor();
		principalExtractor.setSubjectDnRegex(subjectPrincipalRegex);
		this.x509PrincipalExtractor = principalExtractor;
		return this;
	}
public X509Configurer<H> subjectPrincipalRegex(String subjectPrincipalRegex) {
		SubjectDnX509PrincipalExtractor principalExtractor = new SubjectDnX509PrincipalExtractor();
		principalExtractor.setSubjectDnRegex(subjectPrincipalRegex);
		this.x509PrincipalExtractor = principalExtractor;
		return this;
	}
Specifies the regex to extract the principal from the certificate. If not
specified, the default expression from {@link SubjectDnX509PrincipalExtractor} is
used.

@param subjectPrincipalRegex the regex to extract the user principal from the
certificate (i.e. "CN=(.*?)(?:,|$)").
@return the {@link X509Configurer} for further customizations