feat: add configurable prompt backoff

src/utils/password_prompt.py

@@ -13,7 +13,9 @@ Ensure that all dependencies are installed and properly configured in your envir
 
 from utils.seed_prompt import masked_input
 import logging
+import os
 import sys
+import time
 import unicodedata
 
 from termcolor import colored
@@ -28,18 +30,49 @@ colorama_init()
 logger = logging.getLogger(__name__)
 
 
+DEFAULT_MAX_ATTEMPTS = 5
+
+
+def _get_max_attempts(override: int | None = None) -> int:
+    """Return the configured maximum number of prompt attempts."""
+
+    if override is not None:
+        return override
+    env = os.getenv("SEEDPASS_MAX_PROMPT_ATTEMPTS")
+    if env is not None:
+        try:
+            return int(env)
+        except ValueError:
+            pass
+    return DEFAULT_MAX_ATTEMPTS
+
+
+def _apply_backoff(attempts: int, max_attempts: int) -> None:
+    """Sleep using exponential backoff unless disabled."""
+
+    if max_attempts == 0:
+        return
+    delay = 2 ** (attempts - 1)
+    time.sleep(delay)
+
+
 class PasswordPromptError(Exception):
     """Exception raised for password prompt errors."""
 
     pass
 
 
-def prompt_new_password() -> str:
+def prompt_new_password(max_retries: int | None = None) -> str:
     """
     Prompts the user to enter and confirm a new password for encrypting the parent seed.
 
     This function ensures that the password meets the minimum length requirement and that the
-    password and confirmation match. It provides user-friendly messages and handles retries.
+    password and confirmation match. It provides user-friendly messages and handles retries with
+    an exponential backoff between attempts.
+
+    Parameters:
+        max_retries (int | None): Maximum number of attempts before aborting. ``0`` disables the
+            limit. Defaults to the ``SEEDPASS_MAX_PROMPT_ATTEMPTS`` environment variable or ``5``.
 
     Returns:
         str: The confirmed password entered by the user.
@@ -47,10 +80,10 @@ def prompt_new_password() -> str:
     Raises:
         PasswordPromptError: If the user fails to provide a valid password after multiple attempts.
     """
-    max_retries = 5
+    max_retries = _get_max_attempts(max_retries)
     attempts = 0
 
-    while attempts < max_retries:
+    while max_retries == 0 or attempts < max_retries:
         try:
             password = masked_input("Enter a new password: ").strip()
             confirm_password = masked_input("Confirm your password: ").strip()
@@ -61,6 +94,7 @@ def prompt_new_password() -> str:
                 )
                 logging.warning("User attempted to enter an empty password.")
                 attempts += 1
+                _apply_backoff(attempts, max_retries)
                 continue
 
             if len(password) < MIN_PASSWORD_LENGTH:
@@ -74,6 +108,7 @@ def prompt_new_password() -> str:
                     f"User entered a password shorter than {MIN_PASSWORD_LENGTH} characters."
                 )
                 attempts += 1
+                _apply_backoff(attempts, max_retries)
                 continue
 
             if password != confirm_password:
@@ -82,6 +117,7 @@ def prompt_new_password() -> str:
                 )
                 logging.warning("User entered mismatching passwords.")
                 attempts += 1
+                _apply_backoff(attempts, max_retries)
                 continue
 
             # Normalize the password to NFKD form
@@ -99,6 +135,7 @@ def prompt_new_password() -> str:
             )
             print(colored(f"Error: {e}", "red"))
             attempts += 1
+            _apply_backoff(attempts, max_retries)
 
     print(colored("Maximum password attempts exceeded. Exiting.", "red"))
     logging.error("User failed to provide a valid password after multiple attempts.")
@@ -106,16 +143,19 @@ def prompt_new_password() -> str:
 
 
 def prompt_existing_password(
-    prompt_message: str = "Enter your password: ", max_retries: int = 5
+    prompt_message: str = "Enter your password: ", max_retries: int | None = None
 ) -> str:
     """
     Prompt the user for an existing password.
 
-    The user will be reprompted on empty input up to ``max_retries`` times.
+    The user will be reprompted on empty input up to ``max_retries`` times with
+    an exponential backoff between attempts.
 
     Parameters:
         prompt_message (str): Message displayed when prompting for the password.
-        max_retries (int): Number of attempts allowed before aborting.
+        max_retries (int | None): Number of attempts allowed before aborting. ``0``
+            disables the limit. Defaults to the ``SEEDPASS_MAX_PROMPT_ATTEMPTS``
+            environment variable or ``5``.
 
     Returns:
         str: The password provided by the user.
@@ -124,8 +164,9 @@ def prompt_existing_password(
         PasswordPromptError: If the user interrupts the operation or exceeds
             ``max_retries`` attempts.
     """
+    max_retries = _get_max_attempts(max_retries)
     attempts = 0
-    while attempts < max_retries:
+    while max_retries == 0 or attempts < max_retries:
         try:
             password = masked_input(prompt_message).strip()
 
@@ -135,6 +176,7 @@ def prompt_existing_password(
                 )
                 logging.warning("User attempted to enter an empty password.")
                 attempts += 1
+                _apply_backoff(attempts, max_retries)
                 continue
 
             normalized_password = unicodedata.normalize("NFKD", password)
@@ -152,6 +194,7 @@ def prompt_existing_password(
             )
             print(colored(f"Error: {e}", "red"))
             attempts += 1
+            _apply_backoff(attempts, max_retries)
 
     raise PasswordPromptError("Maximum password attempts exceeded")