feat(pii): implement a masking strategy for UPI VPAs (#1641)

Co-authored-by: Prasunna Soppa <prasunna.soppa@juspay.in>
Co-authored-by: Sanchith Hegde <22217505+SanchithHegde@users.noreply.github.com>

crates/common_utils/src/pii.rs

@@ -329,13 +329,33 @@ where
     }
 }
 
+/// Strategy for masking UPI VPA's
+
+#[derive(Debug)]
+pub struct UpiVpaMaskingStrategy;
+
+impl<T> Strategy<T> for UpiVpaMaskingStrategy
+where
+    T: AsRef<str> + std::fmt::Debug,
+{
+    fn fmt(val: &T, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let vpa_str: &str = val.as_ref();
+        if let Some((user_identifier, bank_or_psp)) = vpa_str.split_once('@') {
+            let masked_user_identifier = "*".repeat(user_identifier.len());
+            write!(f, "{masked_user_identifier}@{bank_or_psp}")
+        } else {
+            WithType::fmt(val, f)
+        }
+    }
+}
+
 #[cfg(test)]
 mod pii_masking_strategy_tests {
     use std::str::FromStr;
 
     use masking::{ExposeInterface, Secret};
 
-    use super::{ClientSecret, Email, IpAddress};
+    use super::{ClientSecret, Email, IpAddress, UpiVpaMaskingStrategy};
     use crate::pii::{EmailStrategy, REDACTED};
 
     /*
@@ -435,4 +455,16 @@ mod pii_masking_strategy_tests {
         let secret: Secret<String> = Secret::new("+40712345678".to_string());
         assert_eq!("*** alloc::string::String ***", format!("{secret:?}"));
     }
+
+    #[test]
+    fn test_valid_upi_vpa_masking() {
+        let secret: Secret<String, UpiVpaMaskingStrategy> = Secret::new("my_name@upi".to_string());
+        assert_eq!("*******@upi", format!("{secret:?}"));
+    }
+
+    #[test]
+    fn test_invalid_upi_vpa_masking() {
+        let secret: Secret<String, UpiVpaMaskingStrategy> = Secret::new("my_name_upi".to_string());
+        assert_eq!("*** alloc::string::String ***", format!("{secret:?}"));
+    }
 }