const (
    // HTTPHeaderName is name of HTTP header that carries the token.
    HTTPHeaderName = "X-Delegation-Token-V1"
)

var (
    // ErrMalformedDelegationToken is returned when delegation token cannot be
    // deserialized.
    ErrMalformedDelegationToken = errors.New("auth: malformed delegation token")

    // ErrUnsignedDelegationToken is returned if token's signature cannot be
    // verified.
    ErrUnsignedDelegationToken = errors.New("auth: unsigned delegation token")

    // ErrForbiddenDelegationToken is returned if token is structurally correct,
    // but some of its constraints prevents it from being used. For example, it is
    // already expired or it was minted for some other services, etc. See logs for
    // details.
    ErrForbiddenDelegationToken = errors.New("auth: forbidden delegation token")
)

type CertificatesProvider interface {
    // GetCertificates returns a bundle with certificates of a trusted signer.
    //
    // Returns (nil, nil) if the given signer is not trusted.
    //
    // Returns errors (usually transient) if the bundle can't be fetched.
    GetCertificates(c context.Context, id identity.Identity) (*signing.PublicCertificates, error)
}

type CheckTokenParams struct {
    Token                string               // the delegation token to check
    PeerID               identity.Identity    // identity of the caller, as extracted from its credentials
    CertificatesProvider CertificatesProvider // returns certificates with trusted keys
    GroupsChecker        GroupsChecker        // knows how to do group lookups
    OwnServiceIdentity   identity.Identity    // identity of the current service
}

type GroupsChecker interface {
    // IsMember returns true if the given identity belongs to any of the groups.
    //
    // Unknown groups are considered empty. May return errors if underlying
    // datastore has issues.
    IsMember(c context.Context, id identity.Identity, groups []string) (bool, error)
}