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README.md

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+# sf-auth-gin-middleware
+
+This project provides a small Go library that integrates the Snazzyfellas sf-auth redirect flow with the Gin web framework. It exposes a middleware that enforces authenticated sessions and a prebuilt callback handler that validates sf-auth keys, stores user data in the session, and redirects back to your application.
+
+## Usage
+
+```go
+package main
+
+import (
+    "net/http"
+
+    "github.com/gin-contrib/sessions"
+    "github.com/gin-contrib/sessions/cookie"
+    "github.com/gin-gonic/gin"
+
+    "sf-auth-gin-middleware/sfauthgin"
+)
+
+func main() {
+    router := gin.Default()
+    store := cookie.NewStore([]byte("super-secret"))
+    router.Use(sessions.Sessions("sf_auth", store))
+
+    authMiddleware := sfauthgin.NewMiddleware(func(c *gin.Context) string {
+        return "http://localhost:3000/auth_callback"
+    })
+
+    router.GET("/", func(c *gin.Context) {
+        c.String(http.StatusOK, "Welcome to the demo")
+    })
+
+    router.GET("/auth_callback", sfauthgin.CreateAuthCallbackHandler("/user_info"))
+
+    router.GET("/user_info", authMiddleware, func(c *gin.Context) {
+        session := sessions.Default(c)
+        userID := session.Get("sf_user_id")
+        username := session.Get("sf_username")
+        c.String(http.StatusOK, "User ID: %v\nUsername: %v", userID, username)
+    })
+
+    router.GET("/settings", authMiddleware, func(c *gin.Context) {
+        session := sessions.Default(c)
+        userID := session.Get("sf_user_id")
+        c.String(http.StatusOK, "Settings for user: %v", userID)
+    })
+
+    _ = router.Run(":3000")
+}
+```
+
+## User identity note
+
+Usernames can change, so avoid using `sf_username` as a stable identifier. Store any user-related data under the `sf_user_id` value instead.
+
+If you have many protected routes, you can also attach the middleware to a group, for example:
+
+```go
+protected := router.Group("/")
+protected.Use(authMiddleware)
+protected.GET("/user_info", userInfoHandler)
+protected.GET("/settings", settingsHandler)
+```