Support Customizing Set of OpenSAML Validators

[mathewm3]

Expected Behavior
Option to add/modify/remove SAML20AssertionValidators.attributeValidator especially subjects (BearerSubjectConfirmationValidator) in OpenSaml4AuthenticationProvider.java.

SAML20AssertionValidators.attributeValidator cannot be modified.

Even the method: createDefaultAssertionValidatorWithParameters() does not provide the option to modify SAML20AssertionValidators.attributeValidator

Current Behavior

Currently, it is hardcoded with SAML20AssertionValidators.attributeValidator with default conditions:

1. AudienceRestrictionConditionValidator
2. DelegationRestrictionConditionValidator
3. ConditionValidator
4. ProxyRestrictionConditionValidator

And a subject:

1. BearerSubjectConfirmationValidator

Context

This will give flexibility to take the default assertion validator (createDefaultAssertionValidatorWithParameters) and modify only specific conditions or subjects.