func (v *Validator) SetExpiration(exp time.Time) {
	v.expect()
	v.Expected.Set("exp", exp)
}
SetExpiration sets the "exp" claim per
https://tools.ietf.org/html/rfc7519#section-4.1.4
package jwt
import (
	"time"
	"github.com/SermoDigital/jose/crypto"
)
type JWT interface {
	Claims() Claims
	Validate(key interface{}, method crypto.SigningMethod, v ...*Validator) error
	Serialize(key interface{}) ([]byte, error)
}
type ValidateFunc func(Claims) error
type Validator struct {
	Expected Claims         
	EXP      time.Duration  
	NBF      time.Duration  
	Fn       ValidateFunc   
	_ struct{}  
}
func (v *Validator) Validate(j JWT) error {
	if iss, ok := v.Expected.Issuer(); ok &&
		j.Claims().Get("iss") != iss {
		return ErrInvalidISSClaim
	}
	if sub, ok := v.Expected.Subject(); ok &&
		j.Claims().Get("sub") != sub {
		return ErrInvalidSUBClaim
	}
	if iat, ok := v.Expected.IssuedAt(); ok {
		if t, ok := j.Claims().GetTime("iat"); !t.Equal(iat) || !ok {
			return ErrInvalidIATClaim
		}
	}
	if jti, ok := v.Expected.JWTID(); ok &&
		j.Claims().Get("jti") != jti {
		return ErrInvalidJTIClaim
	}
	if aud, ok := v.Expected.Audience(); ok {
		aud2, ok := j.Claims().Audience()
		if !ok || !ValidAudience(aud, aud2) {
			return ErrInvalidAUDClaim
		}
	}
	if v.Fn != nil {
		return v.Fn(j.Claims())
	}
	return nil
}
func (v *Validator) SetClaim(claim string, val interface{}) {
	v.expect()
	v.Expected.Set(claim, val)
}
func (v *Validator) SetIssuer(iss string) {
	v.expect()
	v.Expected.Set("iss", iss)
}
func (v *Validator) SetSubject(sub string) {
	v.expect()
	v.Expected.Set("sub", sub)
}
func (v *Validator) SetAudience(aud string) {
	v.expect()
	v.Expected.Set("aud", aud)
}