Add is_hexstring to Pcd trait

src/pcd.rs

@@ -276,6 +276,27 @@ pub trait Pcd<'a>: Serialize + Deserialize<'a> {
             Err(Error::msg("No \"roles\" key in this pcd"))
         }
     }
+
+    fn is_hex_string(&self) -> bool { 
+        let value = match serde_json::to_value(self) {
+            Ok(v) => v,
+            Err(_) => return false
+        };
+
+        match value {
+            Value::String(s) => {
+                let vec = Vec::from_hex(&s);
+                if vec.is_err() {
+                    return false;
+                } else if vec.unwrap().len() != 32 {
+                    return false;
+                } else {
+                    return true;
+                }
+            }
+            _ => false
+        }
+    }
 }
 
 impl Pcd<'_> for Value {}