text: # Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
  # SPDX-License-Identifier: MIT-0
  
  import boto3
  import json
  import logging
  import os
  import pymysql
  
  logger = logging.getLogger()
  logger.setLevel(logging.INFO)
  
  
  def lambda_handler(event, context):
      """Secrets Manager RDS MySQL Handler
  
      This handler uses the single-user rotation scheme to rotate an RDS MySQL user credential. This rotation scheme
      logs into the database as the user and rotates the user's own password, immediately invalidating the user's
      previous password.
  
      The Secret SecretString is expected to be a JSON string with the following format:
      {
          'engine': <required: must be set to 'mysql'>,
          'host': <required: instance host name>,
          'username': <required: username>,
          'password': <required: password>,
          'dbname': <optional: database name>,
          'port': <optional: if not specified, default port 3306 will be used>
      }
  
      Args:
          event (dict): Lambda dictionary of event parameters. These keys must include the following:
              - SecretId: The secret ARN or identifier
              - ClientRequestToken: The ClientRequestToken of the secret version
              - Step: The rotation step (one of createSecret, setSecret, testSecret, or finishSecret)
  
          context (LambdaContext): The Lambda runtime information
  
      Raises:
          ResourceNotFoundException: If the secret with the specified arn and stage does not exist
  
          ValueError: If the secret is not properly configured for rotation
  
          KeyError: If the secret json does not contain the expected keys
  
      """
      arn = event['SecretId']
      token = event['ClientRequestToken']
      step = event['Step']
  
      # Setup the client
      service_client = boto3.client('secretsmanager', endpoint_url=os.environ['SECRETS_MANAGER_ENDPOINT'])
  
      # Make sure the version is staged correctly
      metadata = service_client.describe_secret(SecretId=arn)
      if "RotationEnabled" in metadata and not metadata['RotationEnabled']:
          logger.error("Secret %s is not enabled for rotation" % arn)
          raise ValueError("Secret %s is not enabled for rotation" % arn)
      versions = metadata['VersionIdsToStages']
      if token not in versions:
          logger.error("Secret version %s has no stage for rotation of secret %s." % (token, arn))
          raise ValueError("Secret version %s has no stage for rotation of secret %s." % (token, arn))
      if "AWSCURRENT" in versions[token]:
          logger.info("Secret version %s already set as AWSCURRENT for secret %s." % (token, arn))
          return
      elif "AWSPENDING" not in versions[token]:
          logger.error("Secret version %s not set as AWSPENDING for rotation of secret %s." % (token, arn))
          raise ValueError("Secret version %s not set as AWSPENDING for rotation of secret %s." % (token, arn))
  
      # Call the appropriate step
      if step == "createSecret":
          create_secret(service_client, arn, token)
  
      elif step == "setSecret":
          set_secret(service_client, arn, token)
  
      elif step == "testSecret":
          test_secret(service_client, arn, token)
  
      elif step == "finishSecret":
          finish_secret(service_client, arn, token)
  
      else:
          logger.error("lambda_handler: Invalid step parameter %s for secret %s" % (step, arn))
          raise ValueError("Invalid step parameter %s for secret %s" % (step, arn))
  
  
  def create_secret(service_client, arn, token):
      """Generate a new secret
  
      This method first checks for the existence of a secret for the passed in token. If one does not exist, it will generate a
      new secret and put it with the passed in token.
  
      Args:
          service_client (client): The secrets manager service client
  
          arn (string): The secret ARN or other identifier
  
          token (string): The ClientRequestToken associated with the secret version
  
      Raises:
          ValueError: If the current secret is not valid JSON
  
          KeyError: If the secret json does not contain the expected keys
  
      """
      # Make sure the current secret exists
      current_dict = get_secret_dict(service_client, arn, "AWSCURRENT")
  
      # Now try to get the secret version, if that fails, put a new secret
      try:
          get_secret_dict(service_client, arn, "AWSPENDING", token)
          logger.info("createSecret: Successfully retrieved secret for %s." % arn)
      except service_client.exceptions.ResourceNotFoundException:
          # Generate a random password
          passwd = service_client.get_random_password(ExcludeCharacters='/@"\'\\')
          current_dict['password'] = passwd['RandomPassword']
  
          # Put the secret
          service_client.put_secret_value(SecretId=arn, ClientRequestToken=token, SecretString=json.dumps(current_dict), VersionStages=['AWSPENDING'])
          logger.info("createSecret: Successfully put secret for ARN %s and version %s." % (arn, token))
  
  
  def set_secret(service_client, arn, token):
      """Set the pending secret in the database
  
      This method tries to login to the database with the AWSPENDING secret and returns on success. If that fails, it
      tries to login with the AWSCURRENT and AWSPREVIOUS secrets. If either one succeeds, it sets the AWSPENDING password
      as the user password in the database. Else, it throws a ValueError.
  
      Args:
          service_client (client): The secrets manager service client
  
          arn (string): The secret ARN or other identifier
  
          token (string): The ClientRequestToken associated with the secret version
  
      Raises:
          ResourceNotFoundException: If the secret with the specified arn and stage does not exist
  
          ValueError: If the secret is not valid JSON or valid credentials are found to login to the database
  
          KeyError: If the secret json does not contain the expected keys
  
      """
      # First try to login with the pending secret, if it succeeds, return
      pending_dict = get_secret_dict(service_client, arn, "AWSPENDING", token)
      conn = get_connection(pending_dict)
      if conn:
          conn.close()
          logger.info("setSecret: AWSPENDING secret is already set as password in MySQL DB for secret arn %s." % arn)
          return
  
      # Now try the current password
      conn = get_connection(get_secret_dict(service_client, arn, "AWSCURRENT"))
      if not conn:
          # If both current and pending do not work, try previous
          try:
              conn = get_connection(get_secret_dict(service_client, arn, "AWSPREVIOUS"))
          except service_client.exceptions.ResourceNotFoundException:
              conn = None
  
      # If we still don't have a connection, raise a ValueError
      if not conn:
          logger.error("setSecret: Unable to log into database with previous, current, or pending secret of secret arn %s" % arn)
          raise ValueError("Unable to log into database with previous, current, or pending secret of secret arn %s" % arn)
  
      # Now set the password to the pending password
      try:
          with conn.cursor() as cur:
              cur.execute("SET PASSWORD = PASSWORD(%s)", pending_dict['password'])
              conn.commit()
              logger.info("setSecret: Successfully set password for user %s in MySQL DB for secret arn %s." % (pending_dict['username'], arn))
      finally:
          conn.close()
  
  
  def test_secret(service_client, arn, token):
      """Test the pending secret against the database
  
      This method tries to log into the database with the secrets staged with AWSPENDING and runs
      a permissions check to ensure the user has the corrrect permissions.
  
      Args:
          service_client (client): The secrets manager service client
  
          arn (string): The secret ARN or other identifier
  
          token (string): The ClientRequestToken associated with the secret version
  
      Raises:
          ResourceNotFoundException: If the secret with the specified arn and stage does not exist
  
          ValueError: If the secret is not valid JSON or valid credentials are found to login to the database
  
          KeyError: If the secret json does not contain the expected keys
  
      """
      # Try to login with the pending secret, if it succeeds, return
      conn = get_connection(get_secret_dict(service_client, arn, "AWSPENDING", token))
      if conn:
          # This is where the lambda will validate the user's permissions. Uncomment/modify the below lines to
          # tailor these validations to your needs
          try:
              with conn.cursor() as cur:
                  cur.execute("SELECT NOW()")
                  conn.commit()
          finally:
              conn.close()
  
          logger.info("testSecret: Successfully signed into MySQL DB with AWSPENDING secret in %s." % arn)
          return
      else:
          logger.error("testSecret: Unable to log into database with pending secret of secret ARN %s" % arn)
          raise ValueError("Unable to log into database with pending secret of secret ARN %s" % arn)
  
  
  def finish_secret(service_client, arn, token):
      """Finish the rotation by marking the pending secret as current
  
      This method finishes the secret rotation by staging the secret staged AWSPENDING with the AWSCURRENT stage.
  
      Args:
          service_client (client): The secrets manager service client
  
          arn (string): The secret ARN or other identifier
  
          token (string): The ClientRequestToken associated with the secret version
  
      """
      # First describe the secret to get the current version
      metadata = service_client.describe_secret(SecretId=arn)
      current_version = None
      for version in metadata["VersionIdsToStages"]:
          if "AWSCURRENT" in metadata["VersionIdsToStages"][version]:
              if version == token:
                  # The correct version is already marked as current, return
                  logger.info("finishSecret: Version %s already marked as AWSCURRENT for %s" % (version, arn))
                  return
              current_version = version
              break
  
      # Finalize by staging the secret version current
      service_client.update_secret_version_stage(SecretId=arn, VersionStage="AWSCURRENT", MoveToVersionId=token, RemoveFromVersionId=current_version)
      logger.info("finishSecret: Successfully set AWSCURRENT stage to version %s for secret %s." % (version, arn))
  
  
  def get_connection(secret_dict):
      """Gets a connection to MySQL DB from a secret dictionary
  
      This helper function tries to connect to the database grabbing connection info
      from the secret dictionary. If successful, it returns the connection, else None
  
      Args:
          secret_dict (dict): The Secret Dictionary
  
      Returns:
          Connection: The pymysql.connections.Connection object if successful. None otherwise
  
      Raises:
          KeyError: If the secret json does not contain the expected keys
  
      """
      # Parse and validate the secret JSON string
      port = int(secret_dict['port']) if 'port' in secret_dict else 3306
      dbname = secret_dict['dbname'] if 'dbname' in secret_dict else None
  
      # Try to obtain a connection to the db
      try:
          conn = pymysql.connect(secret_dict['host'], user=secret_dict['username'], passwd=secret_dict['password'], port=port, db=dbname, connect_timeout=5)
          return conn
      except pymysql.OperationalError:
          return None
  
  
  def get_secret_dict(service_client, arn, stage, token=None):
      """Gets the secret dictionary corresponding for the secret arn, stage, and token
  
      This helper function gets credentials for the arn and stage passed in and returns the dictionary by parsing the JSON string
  
      Args:
          service_client (client): The secrets manager service client
  
          arn (string): The secret ARN or other identifier
  
          token (string): The ClientRequestToken associated with the secret version, or None if no validation is desired
  
          stage (string): The stage identifying the secret version
  
      Returns:
          SecretDictionary: Secret dictionary
  
      Raises:
          ResourceNotFoundException: If the secret with the specified arn and stage does not exist
  
          ValueError: If the secret is not valid JSON
  
      """
      required_fields = ['host', 'username', 'password']
  
      # Only do VersionId validation against the stage if a token is passed in
      if token:
          secret = service_client.get_secret_value(SecretId=arn, VersionId=token, VersionStage=stage)
      else:
          secret = service_client.get_secret_value(SecretId=arn, VersionStage=stage)
      plaintext = secret['SecretString']
      secret_dict = json.loads(plaintext)
  
      # Run validations against the secret
      if 'engine' not in secret_dict or secret_dict['engine'] != 'mysql':
          raise KeyError("Database engine must be set to 'mysql' in order to use this rotation lambda")
      for field in required_fields:
          if field not in secret_dict:
              raise KeyError("%s key is missing from secret JSON" % field)
  
      # Parse and return the secret JSON string
      return secret_dict
  