Basic create user account

geneit_backend/src/constants.rs

@@ -8,6 +8,11 @@ impl SizeConstraint {
     pub fn new(min: usize, max: usize) -> Self {
         Self { min, max }
     }
+
+    pub fn validate(&self, val: &str) -> bool {
+        let len = val.trim().len();
+        len >= self.min && len <= self.max
+    }
 }
 
 #[derive(Debug, Clone, serde::Serialize)]