CertificateProvider (EU Digital Covid Certificate - Issuance and Validation - 1.0.2)

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
```
@FunctionalInterface
public interface CertificateProvider
```
A functional interface for finding certificates that may be used to verify the signature of a DCC.

Author:

Martin Lindström (martin@idsec.se), Henrik Bengtsson (extern.henrik.bengtsson@digg.se), Henric Norlander (extern.henric.norlander@digg.se)

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`List<X509Certificate>`	`getCertificates(String country, byte[] kid)`	Given a country code and a key identifier the method finds all certificates that matches this criteria.

- Method Detail
  - getCertificates
```
List<X509Certificate> getCertificates(String country,
                                      byte[] kid)
```
    Given a country code and a key identifier the method finds all certificates that matches this criteria.
    At least one of the criteria is set in a call.
    
    If the key identifier (kid) is null the provider should return all certificates for the given country.
    
    If the country code is null the provider should return all certificates matching the key identifier.
    
    Parameters:
    
    country - the two-letter country code
    
    kid - the key identifier
    
    Returns:
    
    a list of certificates (never null)