RefreshTokenValidator (security 3.11.1 API)

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 RefreshTokenValidator
```
Responsible for validating a refresh token is in a valid format. This logic is separate from determining if the refresh token has been revoked or otherwise not present in the persistence layer.

Since:

2.0.0

- Method Summary
  
  All Methods Instance Methods Abstract Methods
  Modifier and Type Method Description
  
  java.util.Optional<java.lang.String> validate(java.lang.String refreshToken)

- Method Detail
  - validate
```
@NonNull
java.util.Optional<java.lang.String> validate(@NonNull
                                              java.lang.String refreshToken)
```
    Parameters:
    
    refreshToken - The refresh token
    
    Returns:
    
    The validated token wrapped in an Optional or Optional#empty() if the supplied token is invalid.