Functionality to remove users from AWS User Pool

[nataliejschultz]

This PR is a continuation of e-mission/e-mission-docs#1008

Copying the following from comment in #45:

I added functionality to remove users who are not in the config file, but are already in the user pool. Previously, I created the user_already_exists function:

def user_already_exists(pool_id, email, cognito_client):
    try:
        response = cognito_client.list_users(UserPoolId=pool_id)
        users = response["Users"]
        result = False
        if str(users).find(email) > 1:
            result = True
        return result
    except ClientError as err:
        logger.error(
            "Couldn't list users for %s. Here's why: %s: %s",
            pool_id,
            err.response["Error"]["Code"],
            err.response["Error"]["Message"],
        )
        raise

this function takes users, which is a list of dictionaries containing info on each user in the pool, and searches for a string matching the desired email.

For the new use case, I modified it a bit to create get_users:

def get_users(pool_id, cognito_client):
    try:
        response = cognito_client.list_users(UserPoolId=pool_id)
        return response["Users"]
    except ClientError as err:
        logger.error(
            "Couldn't list users for %s. Here's why: %s: %s",
            pool_id,
            err.response["Error"]["Code"],
            err.response["Error"]["Message"],
        )
        raise

This function is called early on in the program, and gives us the users variable:
users = get_users(pool_id, cognito_client)

Next, each dictionary in users is looped over, and the email is isolated as user_email.

    for user in users:
        for attr_dict in user["Attributes"]:
            if attr_dict["Name"] == "email":
                user_email = attr_dict["Value"]
                if user_email not in emails:
                    remove_user(pool_id, user_email)
                    print(f"{user_email} removed from pool.")

If the user_email is not in the emails list that was pulled from the config file, another new function named remove_user is called:

def remove_user(pool_id, user):
    response = cognito_client.admin_delete_user(
        UserPoolId= pool_id,
        Username= str(user)
)

I tested this by adding myself to the pool:

email1@nrel.gov not in user pool! Creating account...
Account created! Sending welcome email.

Then trying to re-add myself AND another new email,

email1@nrel.gov already in user pool!
email2@yahoo.com not in user pool! Creating account...
Account created! Sending welcome email.

And finally, removing my first email from the config to see what happens:

email1@nrel.gov removed from pool.
email2@yahoo.com already in user pool!

I checked the user pool, and my email1@nrel.gov was indeed removed from the pool! I decided to try and follow the welcome email to log in with my removed email, just to see what would happen. I got the following message: