console: rework a bit user management

Notably, HTTP headers are configurable and a provider is used for the
frontend side.

console/authentication/middleware.go

@@ -0,0 +1,80 @@
+package authentication
+
+import (
+	"net/http"
+	"reflect"
+
+	"github.com/gin-gonic/gin"
+	"github.com/gin-gonic/gin/binding"
+)
+
+// UserInformation contains information about the current user.
+type UserInformation struct {
+	Login     string `json:"login" header:"LOGIN" binding:"required"`
+	Name      string `json:"name,omitempty" header:"NAME"`
+	Email     string `json:"email,omitempty" header:"EMAIL" binding:"omitempty,email"`
+	LogoutURL string `json:"logout-url,omitempty" header:"LOGOUT" binding:"omitempty,uri"`
+}
+
+// UserAuthentication is a middleware to fill information about the
+// current user. It does not really perform authentication but relies
+// on HTTP headers.
+func (c *Component) UserAuthentication() gin.HandlerFunc {
+	return func(gc *gin.Context) {
+		var info UserInformation
+		if err := gc.ShouldBindWith(&info, customHeaderBinding{c}); err != nil {
+			if c.config.DefaultUser.Login == "" {
+				gc.JSON(http.StatusUnauthorized, gin.H{"message": "No user logged in."})
+				gc.Abort()
+				return
+			}
+			info = c.config.DefaultUser
+		}
+		gc.Set("user", info)
+		gc.Next()
+	}
+}
+
+type customHeaderBinding struct {
+	c *Component
+}
+
+func (customHeaderBinding) Name() string {
+	return "header"
+}
+
+// Bind will bind struct fields to HTTP headers using the configured mapping.
+func (b customHeaderBinding) Bind(req *http.Request, obj interface{}) error {
+	value := reflect.ValueOf(obj).Elem()
+	tValue := reflect.TypeOf(obj).Elem()
+	if value.Kind() != reflect.Struct {
+		panic("should be a struct")
+	}
+	for i := 0; i < tValue.NumField(); i++ {
+		sf := tValue.Field(i)
+		if sf.PkgPath != "" && !sf.Anonymous { // unexported
+			continue
+		}
+		tag := sf.Tag.Get("header")
+		if tag == "" || tag == "-" {
+			continue
+		}
+		var header string
+		switch tag {
+		case "LOGIN":
+			header = b.c.config.Headers.Login
+		case "NAME":
+			header = b.c.config.Headers.Name
+		case "EMAIL":
+			header = b.c.config.Headers.Email
+		case "LOGOUT":
+			header = b.c.config.Headers.LogoutURL
+		}
+		if header == "" {
+			continue
+		}
+		value.Field(i).SetString(req.Header.Get(header))
+	}
+
+	return binding.Validator.ValidateStruct(obj)
+}