update requirements,

001_documentation/Requirements/REQ0016/index.md

@@ -0,0 +1,33 @@
+---
+tags: cms, login-flow
+---
+
+# login flow
+
+## description
+
+```mermaid
+graph TD;
+  Start-->A;
+  A-->B;
+  B-->C;
+  B-->D;
+  D-->E;
+  E-->F;
+  C-->G;
+  G-->A
+
+  F-->End;
+
+  A[greeting, asking username and password]
+  B[check if username and password is valid]
+  C[pasword failed]
+  D[pasword ok]
+  E[login success]
+  F[redirect to '/dashboard']
+
+  G[prompt user wrong username and password]
+
+  Start((start));
+  End((end))
+```