Update comments and Readme

README.md

@@ -393,6 +393,8 @@ param **`networkConnectionCB`** The function that handles the network connection
 
 param **`networkStatusCB`** The function that handle the network connection status acknowledgement.
 
+Due to the client pointer is assigned, to avoid dangling pointer, client should be existed as long as it was used for transportation.
+
 ```cpp
 void setExternalClient(Client *client, ESP_Signer_NetworkConnectionRequestCallback networkConnectionCB,
                            ESP_Signer_NetworkStatusRequestCallback networkStatusCB);
@@ -413,6 +415,8 @@ param **`user`** The GPRS user.
 
 param **`password`** The GPRS password.
 
+Due to the client and modem pointers are assigned, to avoid dangling pointer, client should be existed as long as it was used for transportation.
+
 ```cpp
 void setGSMClient(Client *client, void *modem, const char *pin, const char *apn, const char *user, const char *password);
 ```

examples/Ethernet/Pico/Pico.ino

@@ -179,6 +179,8 @@ void begin()
     config.signer.tokens.scope = "https://www.googleapis.com/auth/spreadsheets,https://www.googleapis.com/auth/drive,https://www.googleapis.com/auth/drive.file";
 
     /* Assign the pointer to global defined external Client object and required callback functions */
+    // Due to the client (eth) pointer is assigned, to avoid dangling pointer, 
+    // client should be existed as long as it was used for transportation.
     Signer.setExternalClient(&eth, networkConnection, networkStatusRequestCallback);
 
     Signer.begin(&config);

examples/GSM/GSM.ino

@@ -165,7 +165,9 @@ void setup()
     config.token_status_callback = tokenStatusCallback;
 
     config.signer.tokens.scope = "https://www.googleapis.com/auth/spreadsheets,https://www.googleapis.com/auth/drive,https://www.googleapis.com/auth/drive.file";
-
+
+    // Due to the gsm_client and modem pointers are assigned, to avoid dangling pointer, 
+    // gsm_client and modem should be existed as long as it was used for transportation.
     Signer.setGSMClient(&gsm_client, &modem, GSM_PIN, apn, gprsUser, gprsPass);
 
     Signer.begin(&config);

src/ESP_Signer.h

@@ -51,6 +51,9 @@ class ESP_Signer
      * @param client The pointer to Arduino Client derived class of SSL Client.
      * @param networkConnectionCB The function that handles the network connection.
      * @param networkStatusCB The function that handle the network connection status acknowledgement.
+     * 
+     * Due to the client pointer is assigned, to avoid dangling pointer, 
+     * client should be existed as long as it was used for transportation.
      */
     void setExternalClient(Client *client, ESP_Signer_NetworkConnectionRequestCallback networkConnectionCB,
                            ESP_Signer_NetworkStatusRequestCallback networkStatusCB)
@@ -66,6 +69,9 @@ class ESP_Signer
      * @param apn The GPRS APN (Access Point Name).
      * @param user The GPRS user.
      * @param password The GPRS password.
+     * 
+     * Due to the client and modem pointers are assigned, to avoid dangling pointer, 
+     * client and modem should be existed as long as it was used for transportation.
      */
     void setGSMClient(Client *client, void *modem = nullptr, const char *pin = nullptr, const char *apn = nullptr, const char *user = nullptr, const char *password = nullptr)
     {