Issue:
Bug: [BUG] adyen connector creates connector's customer reference on the fly



### Bug Description

Connector's customer ID is a unique identifier for a customer's entity in the underlying connector for HyperSwitch for mapping a customer. This identifier is stored under `connector_customer` in `customers` table.

However, for Adyen - this field is a combination of merchant ID and customer ID in HyperSwitch which is unique across different merchants and customers.

This is a blocker for migrated customers whose `shopperReference` (customer ID in Adyen) can be in a different format.

### Expected Behavior

Adyen should rely on the `connector_customer` field for customer and fallback to any default connector specific behavior.

### Actual Behavior

Adyen uses a default behavior for generating `connector_customer_id`

### Steps To Reproduce

--

### Context For The Bug

--

### Environment

--

### Have you spent some time checking if this bug has been raised before?

- [x] I checked and didn't find a similar issue

### Have you read the Contributing Guidelines?

- [x] I have read the [Contributing Guidelines](https://github.com/juspay/hyperswitch/blob/main/docs/CONTRIBUTING.md)

### Are you willing to submit a PR?

None

Pull request description:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
Adyen now uses `connector_customer_id` to form `shopper_reference` if the field is present, else falls to previous implementation.

### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

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2. `crates/router/src/configs`
3. `loadtest/config`
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## Motivation and Context
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## How did you test it?
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<img width="1081" alt="Screenshot 2025-06-24 at 4 01 08 PM" src="https://github.com/user-attachments/assets/08ad7563-b19a-41a5-8729-74aa3b5f6295" />


## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt --all`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible


Testing:

<img width="1081" alt="Screenshot 2025-06-24 at 4 01 08 PM" src="https://github.com/user-attachments/assets/08ad7563-b19a-41a5-8729-74aa3b5f6295" />

Patch:
diff --git a/config/config.example.toml b/config/config.example.toml
index 040e027dcf9..08589cbcc65 100644
--- a/config/config.example.toml
+++ b/config/config.example.toml
@@ -827,7 +827,7 @@ credit = {country = "AU,NZ,CN,HK,IN,LK,KR,MY,SG,GB,BE,FR,DE,IT,ME,NL,PL,ES,ZA,AR
 debit = {country = "AU,NZ,CN,HK,IN,LK,KR,MY,SG,GB,BE,FR,DE,IT,ME,NL,PL,ES,ZA,AR,BR,CO,MX,PA,UY,US,CA", currency = "AFN,ALL,DZD,AOA,ARS,AMD,AWG,AUD,AZN,BSD,BHD,BDT,BBD,BYN,BZD,BMD,BTN,BOB,VES,BAM,BWP,BRL,BND,BGN,BIF,KHR,CAD,CVE,KYD,XAF,CLP,CNY,COP,KMF,CDF,CRC,HRK,CUP,CZK,DKK,DJF,DOP,XCD,EGP,ERN,ETB,EUR,FKP,FJD,XPF,GMD,GEL,GHS,GIP,GTQ,GNF,GYD,HTG,HNL,HKD,HUF,ISK,INR,IDR,IRR,IQD,ILS,JMD,JPY,JOD,KZT,KES,KGS,KWD,LAK,LBP,LSL,LRD,LYD,MOP,MKD,MGA,MWK,MYR,MVR,MRU,MUR,MXN,MDL,MNT,MAD,MZN,MMK,NAD,NPR,ANG,NZD,NIO,NGN,VUV,KPW,NOK,OMR,PKR,PAB,PGK,PYG,PEN,PHP,PLN,GBP,QAR,RON,RUB,RWF,SHP,SVC,WST,STN,SAR,RSD,SCR,SLL,SGD,SBD,SOS,ZAR,KRW,SSP,LKR,SDG,SRD,SZL,SEK,CHF,SYP,TWD,TJS,TZS,THB,TOP,TTD,TND,TRY,TMT,UGX,UAH,AED,USD,UYU,UZS,VND,XOF,YER,ZMW,ZWL"}
 
 [connector_customer]
-connector_list = "gocardless,stax,stripe,facilitapay,hyperswitch_vault"
+connector_list = "adyen,facilitapay,gocardless,hyperswitch_vault,stax,stripe"
 payout_connector_list = "nomupay,stripe,wise"
 
 [bank_config.online_banking_fpx]
diff --git a/config/deployments/integration_test.toml b/config/deployments/integration_test.toml
index 513cb587176..f4c3e3815d0 100644
--- a/config/deployments/integration_test.toml
+++ b/config/deployments/integration_test.toml
@@ -174,7 +174,7 @@ force_cookies = true
 enabled = true
 
 [connector_customer]
-connector_list = "gocardless,stax,stripe,facilitapay,hyperswitch_vault"
+connector_list = "adyen,facilitapay,gocardless,hyperswitch_vault,stax,stripe"
 payout_connector_list = "nomupay,stripe,wise"
 
 [delayed_session_response]
diff --git a/config/deployments/production.toml b/config/deployments/production.toml
index 4b990ad0464..23f5c72e3cd 100644
--- a/config/deployments/production.toml
+++ b/config/deployments/production.toml
@@ -15,7 +15,7 @@ open_banking_uk.adyen.banks = "aib,bank_of_scotland,danske_bank,first_direct,fir
 przelewy24.stripe.banks = "alior_bank,bank_millennium,bank_nowy_bfg_sa,bank_pekao_sa,banki_spbdzielcze,blik,bnp_paribas,boz,citi,credit_agricole,e_transfer_pocztowy24,getin_bank,idea_bank,inteligo,mbank_mtransfer,nest_przelew,noble_pay,pbac_z_ipko,plus_bank,santander_przelew24,toyota_bank,volkswagen_bank"
 
 [connector_customer]
-connector_list = "stax,stripe,gocardless,facilitapay,hyperswitch_vault"
+connector_list = "adyen,facilitapay,gocardless,hyperswitch_vault,stax,stripe"
 payout_connector_list = "nomupay,stripe,wise"
 
 # Connector configuration, provided attributes will be used to fulfill API requests.
diff --git a/config/deployments/sandbox.toml b/config/deployments/sandbox.toml
index d00b12c751f..e09aa5f88fd 100644
--- a/config/deployments/sandbox.toml
+++ b/config/deployments/sandbox.toml
@@ -15,7 +15,7 @@ open_banking_uk.adyen.banks = "aib,bank_of_scotland,danske_bank,first_direct,fir
 przelewy24.stripe.banks = "alior_bank,bank_millennium,bank_nowy_bfg_sa,bank_pekao_sa,banki_spbdzielcze,blik,bnp_paribas,boz,citi,credit_agricole,e_transfer_pocztowy24,getin_bank,idea_bank,inteligo,mbank_mtransfer,nest_przelew,noble_pay,pbac_z_ipko,plus_bank,santander_przelew24,toyota_bank,volkswagen_bank"
 
 [connector_customer]
-connector_list = "stax,stripe,gocardless,facilitapay,hyperswitch_vault"
+connector_list = "adyen,facilitapay,gocardless,hyperswitch_vault,stax,stripe"
 payout_connector_list = "nomupay,stripe,wise"
 
 # Connector configuration, provided attributes will be used to fulfill API requests.
diff --git a/config/development.toml b/config/development.toml
index 95484d6b014..8107dce3886 100644
--- a/config/development.toml
+++ b/config/development.toml
@@ -872,7 +872,7 @@ nexixpay = { payment_method = "card" }
 redsys = { payment_method = "card" }
 
 [connector_customer]
-connector_list = "gocardless,stax,stripe,facilitapay,hyperswitch_vault"
+connector_list = "adyen,facilitapay,gocardless,hyperswitch_vault,stax,stripe"
 payout_connector_list = "nomupay,stripe,wise"
 
 [dummy_connector]
diff --git a/config/docker_compose.toml b/config/docker_compose.toml
index b029fb9987f..484dd76097a 100644
--- a/config/docker_compose.toml
+++ b/config/docker_compose.toml
@@ -883,7 +883,7 @@ card.debit = { connector_list = "cybersource" }
 connector_list = "adyen,archipel,cybersource,novalnet,stripe,worldpay"
 
 [connector_customer]
-connector_list = "gocardless,stax,stripe,facilitapay,hyperswitch_vault"
+connector_list = "adyen,facilitapay,gocardless,hyperswitch_vault,stax,stripe"
 payout_connector_list = "nomupay,stripe,wise"
 
 
diff --git a/crates/hyperswitch_connectors/src/connectors/adyen/transformers.rs b/crates/hyperswitch_connectors/src/connectors/adyen/transformers.rs
index c78daba6c4e..504635fe070 100644
--- a/crates/hyperswitch_connectors/src/connectors/adyen/transformers.rs
+++ b/crates/hyperswitch_connectors/src/connectors/adyen/transformers.rs
@@ -1765,29 +1765,31 @@ type RecurringDetails = (Option<AdyenRecurringModel>, Option<bool>, Option<Strin
 fn get_recurring_processing_model(
     item: &PaymentsAuthorizeRouterData,
 ) -> Result<RecurringDetails, Error> {
-    match (item.request.setup_future_usage, item.request.off_session) {
-        (Some(storage_enums::FutureUsage::OffSession), _) => {
+    let shopper_reference = match item.get_connector_customer_id() {
+        Ok(connector_customer_id) => Some(connector_customer_id),
+        Err(_) => {
             let customer_id = item.get_customer_id()?;
-            let shopper_reference = format!(
+            Some(format!(
                 "{}_{}",
                 item.merchant_id.get_string_repr(),
                 customer_id.get_string_repr()
-            );
+            ))
+        }
+    };
+
+    match (item.request.setup_future_usage, item.request.off_session) {
+        (Some(storage_enums::FutureUsage::OffSession), _) => {
             let store_payment_method = item.request.is_mandate_payment();
             Ok((
                 Some(AdyenRecurringModel::UnscheduledCardOnFile),
                 Some(store_payment_method),
-                Some(shopper_reference),
+                shopper_reference,
             ))
         }
         (_, Some(true)) => Ok((
             Some(AdyenRecurringModel::UnscheduledCardOnFile),
             None,
-            Some(format!(
-                "{}_{}",
-                item.merchant_id.get_string_repr(),
-                item.get_customer_id()?.get_string_repr()
-            )),
+            shopper_reference,
         )),
         _ => Ok((None, None, None)),
     }
@@ -1967,17 +1969,18 @@ fn get_social_security_number(voucher_data: &VoucherData) -> Option<Secret<Strin
     }
 }
 
-fn build_shopper_reference(
-    customer_id: &Option<common_utils::id_type::CustomerId>,
-    merchant_id: common_utils::id_type::MerchantId,
-) -> Option<String> {
-    customer_id.clone().map(|c_id| {
-        format!(
-            "{}_{}",
-            merchant_id.get_string_repr(),
-            c_id.get_string_repr()
-        )
-    })
+fn build_shopper_reference(item: &PaymentsAuthorizeRouterData) -> Option<String> {
+    match item.get_connector_customer_id() {
+        Ok(connector_customer_id) => Some(connector_customer_id),
+        Err(_) => match item.get_customer_id() {
+            Ok(customer_id) => Some(format!(
+                "{}_{}",
+                item.merchant_id.get_string_repr(),
+                customer_id.get_string_repr()
+            )),
+            Err(_) => None,
+        },
+    }
 }
 
 impl TryFrom<(&BankDebitData, &PaymentsAuthorizeRouterData)> for AdyenPaymentMethod<'_> {
@@ -2898,10 +2901,7 @@ impl TryFrom<(&AdyenRouterData<&PaymentsAuthorizeRouterData>, &Card)> for AdyenP
         let amount = get_amount_data(item);
         let auth_type = AdyenAuthType::try_from(&item.router_data.connector_auth_type)?;
         let shopper_interaction = AdyenShopperInteraction::from(item.router_data);
-        let shopper_reference = build_shopper_reference(
-            &item.router_data.customer_id,
-            item.router_data.merchant_id.clone(),
-        );
+        let shopper_reference = build_shopper_reference(item.router_data);
         let (recurring_processing_model, store_payment_method, _) =
             get_recurring_processing_model(item.router_data)?;
         let browser_info = get_browser_info(item.router_data)?;
@@ -3506,10 +3506,7 @@ impl
         let additional_data = get_additional_data(item.router_data);
         let country_code = get_country_code(item.router_data.get_optional_billing());
         let shopper_interaction = AdyenShopperInteraction::from(item.router_data);
-        let shopper_reference = build_shopper_reference(
-            &item.router_data.customer_id,
-            item.router_data.merchant_id.clone(),
-        );
+        let shopper_reference = build_shopper_reference(item.router_data);
         let (recurring_processing_model, store_payment_method, _) =
             get_recurring_processing_model(item.router_data)?;
         let return_url = item.router_data.request.get_router_return_url()?;
@@ -5822,10 +5819,7 @@ impl
         let amount = get_amount_data(item);
         let auth_type = AdyenAuthType::try_from(&item.router_data.connector_auth_type)?;
         let shopper_interaction = AdyenShopperInteraction::from(item.router_data);
-        let shopper_reference = build_shopper_reference(
-            &item.router_data.customer_id,
-            item.router_data.merchant_id.clone(),
-        );
+        let shopper_reference = build_shopper_reference(item.router_data);
         let (recurring_processing_model, store_payment_method, _) =
             get_recurring_processing_model(item.router_data)?;
         let browser_info = get_browser_info(item.router_data)?;
diff --git a/loadtest/config/development.toml b/loadtest/config/development.toml
index 5a59523eeb3..b82746362d0 100644
--- a/loadtest/config/development.toml
+++ b/loadtest/config/development.toml
@@ -554,7 +554,7 @@ gocardless = { long_lived_token = true, payment_method = "bank_debit" }
 billwerk = { long_lived_token = false, payment_method = "card" }
 
 [connector_customer]
-connector_list = "gocardless,stax,stripe,facilitapay,hyperswitch_vault"
+connector_list = "adyen,facilitapay,gocardless,hyperswitch_vault,stax,stripe"
 payout_connector_list = "nomupay,wise"
 
 [dummy_connector]