Where to specify the external id while assuming role

I have a role in another which has the condition

"Condition": {
        "StringEquals": {
          "sts:ExternalId": "12345"
        }
      }

I am using the following session to assume it

def assumed_role_session(role_arn):
    base_session = boto3.session.Session()._session
    fetcher = botocore.credentials.AssumeRoleCredentialFetcher(
        client_creator = base_session.create_client,
        source_credentials = base_session.get_credentials(),
        role_arn = role_arn,
    )
    creds = botocore.credentials.DeferredRefreshableCredentials(
        method = 'assume-role',
        refresh_using = fetcher.fetch_credentials,
        time_fetcher = lambda: datetime.datetime.now(tzlocal())
    )
    botocore_session = botocore.session.Session()
    botocore_session._credentials = creds
    return boto3.Session(botocore_session = botocore_session)

But it is giving authorization issues. Can anyone help with where the external id has to be put?