Get a session token that requires an MFA token with AWS STS using an AWS SDK

The following code example shows how to get a session token that requires an MFA token.

Warning

To avoid security risks, don't use IAM users for authentication when developing purpose-built software or working with real data. Instead, use federation with an identity provider such as AWS IAM Identity Center.

• Create an IAM role that grants permission to list Amazon S3 buckets.

• Create an IAM user that has permission to assume the role only when MFA credentials are provided.

• Register an MFA device for the user.

• Provide MFA credentials to get a session token and use temporary credentials to list S3 buckets.

Python

SDK for Python (Boto3)

Note

There's more on GitHub. Find the complete example and learn how to set up and run in the AWS Code Examples Repository.

Create an IAM user, register an MFA device, and create a role that grants permission to let the user list S3 buckets only when MFA credentials are used.

def setup(iam_resource):
    """
    Creates a new user with no permissions.
    Creates a new virtual multi-factor authentication (MFA) device.
    Displays the QR code to seed the device.
    Asks for two codes from the MFA device.
    Registers the MFA device for the user.
    Creates an access key pair for the user.
    Creates an inline policy for the user that lets the user list Amazon S3 buckets,
    but only when MFA credentials are used.

    Any MFA device that can scan a QR code will work with this demonstration.
    Common choices are mobile apps like LastPass Authenticator,
    Microsoft Authenticator, or Google Authenticator.

    :param iam_resource: A Boto3 AWS Identity and Access Management (IAM) resource
                         that has permissions to create users, MFA devices, and
                         policies in the account.
    :return: The newly created user, user key, and virtual MFA device.
    """
    user = iam_resource.create_user(UserName=unique_name("user"))
    print(f"Created user {user.name}.")

    virtual_mfa_device = iam_resource.create_virtual_mfa_device(
        VirtualMFADeviceName=unique_name("mfa")
    )
    print(f"Created virtual MFA device {virtual_mfa_device.serial_number}")

    print(
        f"Showing the QR code for the device. Scan this in the MFA app of your "
        f"choice."
    )
    with open("qr.png", "wb") as qr_file:
        qr_file.write(virtual_mfa_device.qr_code_png)
    webbrowser.open(qr_file.name)

    print(f"Enter two consecutive code from your MFA device.")
    mfa_code_1 = input("Enter the first code: ")
    mfa_code_2 = input("Enter the second code: ")
    user.enable_mfa(
        SerialNumber=virtual_mfa_device.serial_number,
        AuthenticationCode1=mfa_code_1,
        AuthenticationCode2=mfa_code_2,
    )
    os.remove(qr_file.name)
    print(f"MFA device is registered with the user.")

    user_key = user.create_access_key_pair()
    print(f"Created access key pair for user.")

    print(f"Wait for user to be ready.", end="")
    progress_bar(10)

    user.create_policy(
        PolicyName=unique_name("user-policy"),
        PolicyDocument=json.dumps(
            {
                "Version": "2012-10-17",
                "Statement": [
                    {
                        "Effect": "Allow",
                        "Action": "s3:ListAllMyBuckets",
                        "Resource": "arn:aws:s3:::*",
                        "Condition": {"Bool": {"aws:MultiFactorAuthPresent": True}},
                    }
                ],
            }
        ),
    )
    print(
        f"Created an inline policy for {user.name} that lets the user list buckets, "
        f"but only when MFA credentials are present."
    )

    print("Give AWS time to propagate these new resources and connections.", end="")
    progress_bar(10)

    return user, user_key, virtual_mfa_device

Get temporary session credentials by passing an MFA token, and use the credentials to list S3 buckets for the account.

def list_buckets_with_session_token_with_mfa(mfa_serial_number, mfa_totp, sts_client):
    """
    Gets a session token with MFA credentials and uses the temporary session
    credentials to list Amazon S3 buckets.

    Requires an MFA device serial number and token.

    :param mfa_serial_number: The serial number of the MFA device. For a virtual MFA
                              device, this is an Amazon Resource Name (ARN).
    :param mfa_totp: A time-based, one-time password issued by the MFA device.
    :param sts_client: A Boto3 STS instance that has permission to assume the role.
    """
    if mfa_serial_number is not None:
        response = sts_client.get_session_token(
            SerialNumber=mfa_serial_number, TokenCode=mfa_totp
        )
    else:
        response = sts_client.get_session_token()
    temp_credentials = response["Credentials"]

    s3_resource = boto3.resource(
        "s3",
        aws_access_key_id=temp_credentials["AccessKeyId"],
        aws_secret_access_key=temp_credentials["SecretAccessKey"],
        aws_session_token=temp_credentials["SessionToken"],
    )

    print(f"Buckets for the account:")
    for bucket in s3_resource.buckets.all():
        print(bucket.name)

Destroy the resources created for the demo.

def teardown(user, virtual_mfa_device):
    """
    Removes all resources created during setup.

    :param user: The demo user.
    :param role: The demo MFA device.
    """
    for user_pol in user.policies.all():
        user_pol.delete()
        print("Deleted inline user policy.")
    for key in user.access_keys.all():
        key.delete()
        print("Deleted user's access key.")
    for mfa in user.mfa_devices.all():
        mfa.disassociate()
    virtual_mfa_device.delete()
    user.delete()
    print(f"Deleted {user.name}.")

Run this scenario by using the previously defined functions.

def usage_demo():
    """Drives the demonstration."""
    print("-" * 88)
    print(
        f"Welcome to the AWS Security Token Service assume role demo, "
        f"starring multi-factor authentication (MFA)!"
    )
    print("-" * 88)
    iam_resource = boto3.resource("iam")
    user, user_key, virtual_mfa_device = setup(iam_resource)
    try:
        sts_client = boto3.client(
            "sts", aws_access_key_id=user_key.id, aws_secret_access_key=user_key.secret
        )
        try:
            print("Listing buckets without specifying MFA credentials.")
            list_buckets_with_session_token_with_mfa(None, None, sts_client)
        except ClientError as error:
            if error.response["Error"]["Code"] == "AccessDenied":
                print("Got expected AccessDenied error.")
        mfa_totp = input("Enter the code from your registered MFA device: ")
        list_buckets_with_session_token_with_mfa(
            virtual_mfa_device.serial_number, mfa_totp, sts_client
        )
    finally:
        teardown(user, virtual_mfa_device)
        print("Thanks for watching!")

• For API details, see GetSessionToken in AWS SDK for Python (Boto3) API Reference.