sf-auth-middleware-gin/sfauthgin/sfauth.go

package sfauthgin

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/url"

	"github.com/gin-contrib/sessions"
	"github.com/gin-gonic/gin"
)

const (
	sessionUserIDKey        = "sf_user_id"
	sessionUsernameKey      = "sf_username"
	authenticateURLTemplate = "https://snazzyfellas.com/api/redirect/authenticate?redirect_uri=%s"
	validateURL             = "https://snazzyfellas.com/api/redirect/validate"
)

type validationRequest struct {
	UserID string `json:"user_id"`
	Key    string `json:"key"`
}

type validationResponse struct {
	Valid  bool   `json:"valid"`
	UserID string `json:"user_id"`
}

// NewMiddleware creates a Gin middleware that checks for sf-auth session values
// and redirects to the Snazzyfellas authenticate endpoint when missing.
func NewMiddleware(redirectURL func(*gin.Context) string) gin.HandlerFunc {
	return func(c *gin.Context) {
		session := sessions.Default(c)
		if session == nil {
			c.String(http.StatusInternalServerError, "session middleware not configured")
			c.Abort()
			return
		}

		userID := session.Get(sessionUserIDKey)
		username := session.Get(sessionUsernameKey)
		if !isNonEmptyString(userID) || !isNonEmptyString(username) {
			target := ""
			if redirectURL != nil {
				target = redirectURL(c)
			}
			if target == "" {
				c.String(http.StatusInternalServerError, "redirect URL is required")
				c.Abort()
				return
			}

			redirect := fmt.Sprintf(authenticateURLTemplate, url.QueryEscape(target))
			c.Redirect(http.StatusFound, redirect)
			c.Abort()
			return
		}

		c.Next()
	}
}

// CreateAuthCallbackHandler returns a handler for the sf-auth callback route.
// It validates the one-time key, stores session values, and redirects to redirectTo.
func CreateAuthCallbackHandler(redirectTo string) gin.HandlerFunc {
	return func(c *gin.Context) {
		if redirectTo == "" {
			c.String(http.StatusInternalServerError, "redirect destination is required")
			return
		}

		userID := c.Query("user_id")
		username := c.Query("username")
		key := c.Query("key")
		if userID == "" || username == "" || key == "" {
			c.String(http.StatusBadRequest, "missing required query parameters")
			return
		}

		if err := validateAuth(c, userID, key); err != nil {
			c.String(http.StatusUnauthorized, err.Error())
			return
		}

		session := sessions.Default(c)
		if session == nil {
			c.String(http.StatusInternalServerError, "session middleware not configured")
			return
		}

		session.Set(sessionUserIDKey, userID)
		session.Set(sessionUsernameKey, username)
		if err := session.Save(); err != nil {
			c.String(http.StatusInternalServerError, "failed to save session")
			return
		}

		c.Redirect(http.StatusFound, redirectTo)
	}
}

func validateAuth(c *gin.Context, userID string, key string) error {
	payload := validationRequest{UserID: userID, Key: key}
	body, err := json.Marshal(payload)
	if err != nil {
		return errors.New("failed to encode validation payload")
	}

	req, err := http.NewRequestWithContext(c.Request.Context(), http.MethodPost, validateURL, bytes.NewReader(body))
	if err != nil {
		return errors.New("failed to create validation request")
	}
	req.Header.Set("Content-Type", "application/json")

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return errors.New("failed to reach validation service")
	}
	defer resp.Body.Close()

	if resp.StatusCode < http.StatusOK || resp.StatusCode >= http.StatusMultipleChoices {
		return fmt.Errorf("validation service returned status %d", resp.StatusCode)
	}

	var result validationResponse
	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
		return errors.New("invalid validation response")
	}

	if !result.Valid || result.UserID != userID {
		return errors.New("invalid auth response")
	}

	return nil
}

func isNonEmptyString(value interface{}) bool {
	text, ok := value.(string)
	if !ok {
		return false
	}
	return text != ""
}