type option func(*Foo) interface{}

// Verbosity sets Foo's verbosity level to v.
func Verbosity(v int) option {
    return func(f *Foo) interface{} {
        previous := f.verbosity
        f.verbosity = v
        return previous
    }
}

// Option sets the options specified.
// It returns the previous value of the last argument.
func (f *Foo) Option(opts ...option) (previous interface{}) {
    for _, opt := range opts {
        previous = opt(f)
    }
    return previous
}

// https://github.com/ory/fosite/blob/v0.29.6/oauth2.go#L42-L161

// OAuth2Provider is an interface that enables you to write OAuth2 handlers with only a few lines of code.
// Check fosite.Fosite for an implementation of this interface.
type OAuth2Provider interface {
	NewAuthorizeRequest(ctx context.Context, req *http.Request) (AuthorizeRequester, error)

	NewAuthorizeResponse(ctx context.Context, requester AuthorizeRequester, session Session) (AuthorizeResponder, error)

	WriteAuthorizeError(rw http.ResponseWriter, requester AuthorizeRequester, err error)

	WriteAuthorizeResponse(rw http.ResponseWriter, requester AuthorizeRequester, responder AuthorizeResponder)
	
	NewAccessRequest(ctx context.Context, req *http.Request, session Session) (AccessRequester, error)

	// ...
}

// https://github.com/ory/fosite/blob/v0.29.6/fosite.go#L85-L105

// Fosite implements OAuth2Provider.
type Fosite struct {
	Store                      Storage
	AuthorizeEndpointHandlers  AuthorizeEndpointHandlers
	TokenEndpointHandlers      TokenEndpointHandlers
	TokenIntrospectionHandlers TokenIntrospectionHandlers
	RevocationHandlers         RevocationHandlers
	Hasher                     Hasher
	ScopeStrategy              ScopeStrategy
	AudienceMatchingStrategy   AudienceMatchingStrategy
	JWKSFetcherStrategy        JWKSFetcherStrategy
	HTTPClient                 *http.Client

	// TokenURL is the the URL of the Authorization Server's Token Endpoint.
	TokenURL string

	// SendDebugMessagesToClients if set to true, includes error debug messages in response payloads. Be aware that sensitive
	// data may be exposed, depending on your implementation of Fosite. Such sensitive data might include database error
	// codes or other information. Proceed with caution!
	SendDebugMessagesToClients bool
}

// https://github.com/ory/fosite/blob/v0.29.6/access_request_handler.go#L87-L101

func (f *Fosite) NewAccessRequest(ctx context.Context, r *http.Request, session Session) (AccessRequester, error) {
	// 前処理
	
	var found bool = false
	for _, loader := range f.TokenEndpointHandlers {
		if err := loader.HandleTokenEndpointRequest(ctx, accessRequest); err == nil {
			found = true
		} else if errors.Cause(err).Error() == ErrUnknownRequest.Error() {
			// do nothing
		} else if err != nil {
			return accessRequest, err
		}
	}

	if !found {
		return nil, errors.WithStack(ErrInvalidRequest)
	}
	return accessRequest, nil
}

https://github.com/ory/fosite/blob/v0.29.6/compose/compose.go#L33-L91

type Factory func(config *Config, storage interface{}, strategy interface{}) interface{}


// Compose takes a config, a storage, a strategy and handlers to instantiate an OAuth2Provider:
// ...
func Compose(config *Config, storage interface{}, strategy interface{}, hasher fosite.Hasher, factories ...Factory) fosite.OAuth2Provider {
	if hasher == nil {
		hasher = &fosite.BCrypt{WorkFactor: config.GetHashCost()}
	}

	f := &fosite.Fosite{
		Store:                      storage.(fosite.Storage),
		AuthorizeEndpointHandlers:  fosite.AuthorizeEndpointHandlers{},
		TokenEndpointHandlers:      fosite.TokenEndpointHandlers{},
		TokenIntrospectionHandlers: fosite.TokenIntrospectionHandlers{},
		RevocationHandlers:         fosite.RevocationHandlers{},
		Hasher:                     hasher,
		ScopeStrategy:              config.GetScopeStrategy(),
		AudienceMatchingStrategy:   config.GetAudienceStrategy(),
		SendDebugMessagesToClients: config.SendDebugMessagesToClients,
		TokenURL:                   config.TokenURL,
		JWKSFetcherStrategy:        config.GetJWKSFetcherStrategy(),
	}

	for _, factory := range factories {
		res := factory(config, storage, strategy)
		if ah, ok := res.(fosite.AuthorizeEndpointHandler); ok {
			f.AuthorizeEndpointHandlers.Append(ah)
		}
		if th, ok := res.(fosite.TokenEndpointHandler); ok {
			f.TokenEndpointHandlers.Append(th)
		}
		if tv, ok := res.(fosite.TokenIntrospector); ok {
			f.TokenIntrospectionHandlers.Append(tv)
		}
		if rh, ok := res.(fosite.RevocationHandler); ok {
			f.RevocationHandlers.Append(rh)
		}
	}

	return f
}

// https://github.com/ory/fosite/blob/v0.29.6/compose/compose_oauth2.go

// OAuth2ClientCredentialsGrantFactory creates an OAuth2 client credentials grant handler and registers
// an access token, refresh token and authorize code validator.
func OAuth2ClientCredentialsGrantFactory(config *Config, storage interface{}, strategy interface{}) interface{} {
	return &oauth2.ClientCredentialsGrantHandler{
		HandleHelper: &oauth2.HandleHelper{
			AccessTokenStrategy: strategy.(oauth2.AccessTokenStrategy),
			AccessTokenStorage:  storage.(oauth2.AccessTokenStorage),
			AccessTokenLifespan: config.GetAccessTokenLifespan(),
		},
		ScopeStrategy:            config.GetScopeStrategy(),
		AudienceMatchingStrategy: config.GetAudienceStrategy(),
	}
}

// https://github.com/ory/fosite/blob/v0.29.6/compose/compose_openid.go

// OpenIDConnectRefreshFactory creates a handler for refreshing openid connect tokens.
//
// **Important note:** You must add this handler *after* you have added an OAuth2 authorize code handler!
func OpenIDConnectRefreshFactory(config *Config, storage interface{}, strategy interface{}) interface{} {
	return &openid.OpenIDConnectRefreshHandler{
		IDTokenHandleHelper: &openid.IDTokenHandleHelper{
			IDTokenStrategy: strategy.(openid.OpenIDConnectTokenStrategy),
		},
	}
}

// https://github.com/ory/fosite/blob/v0.29.6/compose/compose.go#L93-L122

// ComposeAllEnabled returns a fosite instance with all OAuth2 and OpenID Connect handlers enabled.
func ComposeAllEnabled(config *Config, storage interface{}, secret []byte, key *rsa.PrivateKey) fosite.OAuth2Provider {
	return Compose(
		config,
		storage,
		&CommonStrategy{
			CoreStrategy:               NewOAuth2HMACStrategy(config, secret, nil),
			OpenIDConnectTokenStrategy: NewOpenIDConnectStrategy(config, key),
			JWTStrategy: &jwt.RS256JWTStrategy{
				PrivateKey: key,
			},
		},
		nil,

		OAuth2AuthorizeExplicitFactory,
		OAuth2AuthorizeImplicitFactory,
		OAuth2ClientCredentialsGrantFactory,
		OAuth2RefreshTokenGrantFactory,
		OAuth2ResourceOwnerPasswordCredentialsFactory,

		OpenIDConnectExplicitFactory,
		OpenIDConnectImplicitFactory,
		OpenIDConnectHybridFactory,
		OpenIDConnectRefreshFactory,

		OAuth2TokenIntrospectionFactory,

		OAuth2PKCEFactory,
	)
}