decrypt_user_auth_token.py

def decrypt_user_auth_token(encrypted_token):
    
    # Decode the base64
    encrypted_token = base64.b64decode(encrypted_token)

    # Initialize KMS client
    kms = boto3.client('kms', region_name='us-east-1')
    
    # Read the CMK key alias from the environment variable
    cmk_key_alias = os.environ.get("CMK_ALIAS")

    # Decrypt the token
    response = kms.decrypt(
        KeyId=cmk_key_alias,
        CiphertextBlob=encrypted_token
    )
    
    # Store accessToken in variable
    accessToken = response["Plaintext"].decode("utf-8")
    
    # Send the accessToken back
    return accessToken