Add token creation (login)

common/privileges.go

@@ -98,3 +98,31 @@ func (p Privileges) String() string {
 	}
 	return strings.Join(pvs, ", ")
 }
+
+var privilegeMustBe = [...]int{
+	1,
+	1,
+	1,
+	3,
+	3,
+	4,
+	4,
+	4,
+	4,
+	4,
+	3,
+}
+
+// CanOnly removes any privilege that the user has requested to have, but cannot have due to their rank.
+func (p Privileges) CanOnly(rank int) Privileges {
+	newPrivilege := 0
+	for i, v := range privilegeMustBe {
+		wants := p&1 == 1
+		can := rank >= v
+		if wants && can {
+			newPrivilege |= 1 << uint(i)
+		}
+		p >>= 1
+	}
+	return Privileges(newPrivilege)
+}