@Override
    @CanIgnoreReturnValue
    public AuthenticationResultBuilder collect(final Authentication authentication) {
        Optional.ofNullable(authentication).ifPresent(authentications::add);
        return this;
    }
Principal id is and must be enforced to be the same for all authentications.
Based on that restriction, it's safe to grab the first principal id in the chain
when composing the authentication chain for the caller.
core/cas-server-core-authentication-api/src/main/java/org/apereo/cas/authentication/DefaultAuthenticationResultBuilder.java