1 files changed, 183 insertions, 0 deletions
diff --git a/cmd/monfront/authenticater.go b/cmd/monfront/authenticater.go
new file mode 100644
index 0000000..8453264
--- /dev/null
+++ b/cmd/monfront/authenticater.go
@@ -0,0 +1,183 @@
+package main
+
+import (
+	"crypto/hmac"
+	"crypto/rand"
+	"crypto/sha256"
+	"database/sql"
+	"encoding/base64"
+	"fmt"
+	"log"
+	"net/http"
+	"strings"
+	"time"
+)
+
+const (
+	BasicAuthPrompt = `Basic realm="auth for monfront"`
+	SessionCookie   = `session`
+	UserAnonymous   = `anonymous`
+)
+
+type (
+	// Authenticator is a middleware taking a context and authenticating
+	// the user.
+	Authenticator struct {
+		db             *sql.DB
+		Mode           string
+		Token          []byte
+		AllowAnonymous bool
+		Header         string
+		List           [][]string
+		ClientCA       string
+
+		sessions map[string]*session // maps a session key to a user
+	}
+
+	session struct {
+		user string
+		t    time.Time
+	}
+)
+
+// Handler returns the handler for the authentication configuration.
+func (a *Authenticator) Handler() (func(*Context) error, error) {
+	switch a.Mode {
+	case "none":
+		return func(_ *Context) error { return nil }, nil
+	case "header":
+		if a.Header == "" {
+			return nil, fmt.Errorf("authentication mode is 'header' but no header was provided")
+		}
+		return func(c *Context) error {
+			if user := c.r.Header.Get(a.Header); user == "" {
+				if a.AllowAnonymous {
+					c.User = UserAnonymous
+					return nil
+				}
+				return a.Unauthorized(c)
+			} else {
+				c.User = user
+			}
+			return nil
+		}, nil
+	case "list":
+		return func(c *Context) error {
+			user, pass, ok := c.r.BasicAuth()
+			if !ok || user == "" || pass == "" {
+				if a.AllowAnonymous {
+					c.User = UserAnonymous
+					return nil
+				}
+				c.w.Header().Set("WWW-Authenticate", BasicAuthPrompt)
+				return a.Unauthorized(c)
+			}
+			var found string
+			for _, entry := range a.List {
+				if entry[0] == user {
+					found = entry[1]
+				}
+			}
+			if found == "" {
+				c.w.Header().Set("WWW-Authenticate", BasicAuthPrompt)
+				return a.Unauthorized(c)
+			}
+			p := pwHash{}
+			if err := p.Parse(found); err != nil {
+				log.Printf("could not parse hash for user '%s': %s", user, err)
+				return a.Unauthorized(c)
+			}
+			if ok, err := p.compare(pass); err != nil {
+				c.w.Header().Set("WWW-Authenticate", BasicAuthPrompt)
+				return a.Unauthorized(c)
+			} else if !ok {
+				c.w.Header().Set("WWW-Authenticate", BasicAuthPrompt)
+				return a.Unauthorized(c)
+			}
+			c.User = user
+			return nil
+		}, nil
+	case "db":
+		return func(c *Context) error {
+			sessCookie := c.GetCookieVal(SessionCookie)
+			if sessCookie != "" {
+				ses := a.getSession(sessCookie)
+				if ses != "" {
+					// TODO fix time limit to make it variable
+					c.SetCookie(SessionCookie, sessCookie, time.Now().Add(2*time.Hour))
+					c.User = ses
+					return nil
+				}
+			}
+			return fmt.Errorf("NOT YET IMPLEMENTED")
+		}, fmt.Errorf("NOT YET IMPLEMENTED")
+	case "cert":
+		return func(c *Context) error {
+			return fmt.Errorf("NOT YET IMPLEMENTED")
+		}, fmt.Errorf("NOT YET IMPLEMENTED")
+	default:
+		return nil, fmt.Errorf("unknown mode '%s' for authentication", a.Mode)
+	}
+	return nil, fmt.Errorf("could not create authenticator")
+}
+
+func (a *Authenticator) Unauthorized(c *Context) error {
+	c.w.WriteHeader(http.StatusUnauthorized)
+	fmt.Fprintf(c.w, "unauthorized\n")
+	return fmt.Errorf("no authentication")
+}
+
+// creates a session for a user
+func (a *Authenticator) createSession(user string) (string, error) {
+	raw := make([]byte, 32)
+	if _, err := rand.Read(raw); err != nil {
+		return "", fmt.Errorf("could not generate new session key")
+	}
+	res := a.mac(raw)
+	ses := fmt.Sprintf(
+		"%s-%s",
+		base64.StdEncoding.EncodeToString(raw),
+		base64.StdEncoding.EncodeToString(res),
+	)
+	a.sessions[ses] = &session{user: user, t: time.Now()}
+	return ses, nil
+}
+
+func (a *Authenticator) mac(input []byte) []byte {
+	mac := hmac.New(sha256.New, a.Token)
+	mac.Write(input)
+	return mac.Sum(nil)
+}
+
+// getSession returns the username of the current session.
+func (a *Authenticator) getSession(session string) string {
+	if session == "" {
+		return ""
+	}
+	parts := strings.Split(session, "-")
+	if len(parts) != 2 {
+		return ""
+	}
+	msg, err := base64.StdEncoding.DecodeString(parts[0])
+	if err != nil {
+		return ""
+	}
+	mac, err := base64.StdEncoding.DecodeString(parts[1])
+	if err != nil {
+		return ""
+	}
+	verify := a.mac(msg)
+	if !hmac.Equal(mac, verify) {
+		return ""
+	}
+	if ses, found := a.sessions[session]; found {
+		// TODO make timeout a config option
+		if time.Now().Sub(ses.t) < 8*time.Hour {
+			delete(a.sessions, session)
+			return ""
+		}
+		ses.t = time.Now()
+		return ses.user
+	}
+	return ""
+}