Start writing purple auth source

cmd/purple-tulip/server/auth-source.go

@@ -0,0 +1,32 @@
+package server
+
+import (
+	"github.com/1f349/mjwt"
+	"github.com/1f349/mjwt/auth"
+	"github.com/1f349/tulip/database"
+	"github.com/1f349/tulip/oauth"
+	"net/http"
+)
+
+type PurpleAuthSource struct {
+	DB     *database.DB
+	Signer mjwt.Signer
+}
+
+var _ oauth.AuthSource = &PurpleAuthSource{}
+
+func (p *PurpleAuthSource) UserAuthorization(rw http.ResponseWriter, req *http.Request) (string, error) {
+	c := req.Cookie("auth")
+	if c.Value == "" {
+		http.Error(rw, "No auth", http.StatusForbidden)
+		return
+	}
+
+	_, b, err := mjwt.ExtractClaims[auth.AccessTokenClaims](p.Signer, c.Value)
+	if err != nil {
+		http.Error(rw, "Invalid token", http.StatusForbidden)
+		return
+	}
+
+	if b.Issuer!=
+}