gothic.go

/* Based on https://github.com/markbates/goth/blob/edc3e96387cb58c3f3d58e70db2f115815ccdf1e/gothic/gothic.go */
package echogothic

import (
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"os"

	"github.com/gorilla/sessions"
	"github.com/labstack/echo/v4"
	"github.com/markbates/goth"
	"github.com/markbates/goth/gothic"
)

var defaultStore sessions.Store
var keySet = false

func init() {
	key := []byte(os.Getenv("SESSION_SECRET"))
	keySet = len(key) != 0
    defaultStore = gothic.Store
}

/*
BeginAuthHandler is a convenience handler for starting the authentication process.
It expects to be able to get the name of the provider from the query parameters
as either "provider" or ":provider".

BeginAuthHandler will redirect the user to the appropriate authentication end-point
for the requested provider.
*/
func BeginAuthHandler(ectx echo.Context) error {
	url, err := GetAuthURL(ectx)
	if err != nil {
		return err
	}

	return ectx.Redirect(http.StatusTemporaryRedirect, url)
}

// SetState sets the state string associated with the given request.
// If no state string is associated with the request, one will be generated.
// This state is sent to the provider and can be retrieved during the
// callback.
var SetState = func(ectx echo.Context) string {
	return gothic.SetState(ectx.Request())
}

// GetState gets the state returned by the provider during the callback.
// This is used to prevent CSRF attacks, see
// http://tools.ietf.org/html/rfc6749#section-10.12
var GetState = func(ectx echo.Context) string {
	return gothic.GetState(ectx.Request())
}

/*
GetAuthURL starts the authentication process with the requested provided.
It will return a URL that should be used to send users to.

It expects to be able to get the name of the provider from the query parameters
as either "provider" or ":provider".

I would recommend using the BeginAuthHandler instead of doing all of these steps
yourself, but that's entirely up to you.
*/
func GetAuthURL(ectx echo.Context) (string, error) {
	if !keySet && defaultStore == gothic.Store {
		fmt.Println("goth/gothic: no SESSION_SECRET environment variable is set. The default cookie store is not available and any calls will fail. Ignore this warning if you are using a different store.")
	}
	providerName, err := GetProviderName(ectx)
	if err != nil {
		return "", err
	}

	provider, err := goth.GetProvider(providerName)
	if err != nil {
		return "", err
	}
	sess, err := provider.BeginAuth(SetState(ectx))
	if err != nil {
		return "", err
	}

	url, err := sess.GetAuthURL()
	if err != nil {
		return "", err
	}

	err = StoreInSession(providerName, sess.Marshal(), ectx)

	if err != nil {
		return "", err
	}

	return url, err
}

/*
CompleteUserAuth does what it says on the tin. It completes the authentication
process and fetches all of the basic information about the user from the provider.

It expects to be able to get the name of the provider from the query parameters
as either "provider" or ":provider".
*/
var CompleteUserAuth = func(ectx echo.Context) (goth.User, error) {
    if !keySet && defaultStore == gothic.Store {
		fmt.Println("goth/gothic: no SESSION_SECRET environment variable is set. The default cookie store is not available and any calls will fail. Ignore this warning if you are using a different store.")
	}
	defer func() {
		// TODO: log?
		_ = Logout(ectx)
	}()

	providerName, err := GetProviderName(ectx)
	if err != nil {
		return goth.User{}, err
	}

	provider, err := goth.GetProvider(providerName)
	if err != nil {
		return goth.User{}, err
	}

	value, err := GetFromSession(providerName, ectx)
	if err != nil {
		return goth.User{}, err
	}

	sess, err := provider.UnmarshalSession(value)
	if err != nil {
		return goth.User{}, err
	}

	err = validateState(ectx, sess)
	if err != nil {
		return goth.User{}, err
	}

	user, err := provider.FetchUser(sess)
	if err == nil {
		// user can be found with existing session data
		return user, err
	}

	params := ectx.Request().URL.Query()
	if params.Encode() == "" && ectx.Request().Method == "POST" {
		err = ectx.Request().ParseForm()
		if err != nil {
			return goth.User{}, err
		}
		params = ectx.Request().Form
	}

	// get new token and retry fetch
	_, err = sess.Authorize(provider, params)
	if err != nil {
		return goth.User{}, err
	}

	err = StoreInSession(providerName, sess.Marshal(), ectx)

	if err != nil {
		return goth.User{}, err
	}

	gu, err := provider.FetchUser(sess)
	return gu, err
}

// validateState ensures that the state token param from the original
// AuthURL matches the one included in the current (callback) request.
func validateState(ectx echo.Context, sess goth.Session) error {
	rawAuthURL, err := sess.GetAuthURL()
	if err != nil {
		return err
	}

	authURL, err := url.Parse(rawAuthURL)
	if err != nil {
		return err
	}

	reqState := GetState(ectx)

	originalState := authURL.Query().Get("state")
	if originalState != "" && (originalState != reqState) {
		return errors.New("state token mismatch")
	}
	return nil
}

// Logout invalidates a user session.
func Logout(ectx echo.Context) error {
	return gothic.Logout(ectx.Response(), ectx.Request())
}

// GetProviderName is a function used to get the name of a provider
// for a given request. By default, this provider is fetched from
// the URL query string. If you provide it in a different way,
// assign your own function to this variable that returns the provider
// name for your request.
var GetProviderName = getProviderName

func getProviderName(ectx echo.Context) (string, error) {

	if p := ectx.Param("provider"); p != "" {
		return p, nil
	}

	return gothic.GetProviderName(ectx.Request())
}

// StoreInSession stores a specified key/value pair in the session.
func StoreInSession(key string, value string, ectx echo.Context) error {
	return gothic.StoreInSession(key, value, ectx.Request(), ectx.Response())
}

// GetFromSession retrieves a previously-stored value from the session.
// If no value has previously been stored at the specified key, it will return an error.
func GetFromSession(key string, ectx echo.Context) (string, error) {
	return gothic.GetFromSession(key, ectx.Request())
}