text: <user>
  Create a function block for user authentication in TwinCAT Structured Text<|endoftext|>
  <assistant>
  FUNCTION_BLOCK FB_UserAuthentication
  VAR_INPUT
      sUsername       : STRING(50);   // Input username
      sPassword       : STRING(50);   // Input password
      bRememberMe     : BOOL;         // Remember user option
      bLogin          : BOOL;         // Trigger login process
      bResetPassword  : BOOL;         // Trigger password reset
  END_VAR
  
  VAR_OUTPUT
      bAuthSuccess    : BOOL;         // Authentication success flag
      bAuthError      : BOOL;         // Authentication error flag
      nErrorID        : UDINT;        // Error ID for troubleshooting
      sErrorMessage   : STRING(100);  // Human-readable error message
  END_VAR
  
  VAR
      fbStringCompare : FB_StringCompare;  // String comparison function block
      fbMD5           : FB_MD5;            // MD5 hashing function block
      sHashedPassword : STRING(32);        // MD5 hashed password
      fbFileRead      : FB_FileRead;       // File reading function block
      fbFileWrite     : FB_FileWrite;      // File writing function block
      sUserDataFile   : STRING := 'C:\UserData.csv';  // User data storage file
  END_VAR
  
  // Main program organization unit (POU)
  METHOD Main
  VAR_INPUT
  END_VAR
  // =========================================================
  
  // Reset output variables
  bAuthSuccess := FALSE;
  bAuthError := FALSE;
  nErrorID := 0;
  sErrorMessage := '';
  
  // Perform login when triggered
  IF bLogin THEN
      // Hash the input password
      fbMD5(sMessage := sPassword, bExecute := TRUE);
      IF fbMD5.bBusy THEN
          RETURN;
      END_IF
      sHashedPassword := fbMD5.sHash;
  
      // Read user data from file
      fbFileRead(sPathName := sUserDataFile, bExecute := TRUE);
      IF fbFileRead.bBusy THEN
          RETURN;
      END_IF
  
      // Compare username and hashed password
      fbStringCompare(sSearchString := CONCAT(sUsername, ',', sHashedPassword), 
                      sMainString := fbFileRead.sContent, 
                      bExecute := TRUE);
  
      IF fbStringCompare.bMatch THEN
          bAuthSuccess := TRUE;
          
          // Update "Remember Me" status if selected
          IF bRememberMe THEN
              // Implementation for remembering user (e.g., writing to a cookie file)
              // Note: This is a simplified example and may not be secure for production use
              fbFileWrite(sPathName := 'C:\RememberMe.txt', 
                          sContent := sUsername, 
                          bExecute := TRUE);
          END_IF
      ELSE
          bAuthError := TRUE;
          nErrorID := 1;
          sErrorMessage := 'Invalid username or password';
      END_IF
  END_IF
  
  // Handle password reset request
  IF bResetPassword THEN
      // Implementation for password reset (e.g., sending reset link to user's email)
      // Note: This is a placeholder and would require additional functionality
      bAuthError := TRUE;
      nErrorID := 2;
      sErrorMessage := 'Password reset functionality not implemented';
  END_IF
  
  // =========================================================
  END_METHOD
  
  // Brief explanation of the implemented PLC software concept:
  // This function block implements a basic user authentication system using TwinCAT 3 Structured Text.
  // It handles user login by comparing input credentials against stored data, implements password hashing for security,
  // and provides a framework for "Remember Me" and password reset functionalities.
  
  // Suggested TwinCAT 3 features or programming techniques to enhance the implementation:
  // 1. Use TwinCAT's encryption libraries for more robust password hashing and security.
  // 2. Implement TwinCAT HMI for a user-friendly login interface.
  // 3. Utilize TwinCAT Database Server for more efficient and secure user data storage and retrieval.<|endoftext|>
  