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Castle protects your users from account compromise

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Castle analyzes device, location, and interaction patterns in your web and mobile apps and lets you stop account takeover attacks in real-time.


pip install castle


import and configure the library with your Castle API secret.

from castle.configuration import configuration, DEFAULT_ALLOWLIST

# Same as setting it through Castle.api_secret
configuration.api_secret = ':YOUR-API-SECRET'

# For authenticate method you can set failover strategies: allow(default), deny, challenge, throw
configuration.failover_strategy = 'deny'

# Castle::RequestError is raised when timing out in milliseconds (default: 500 milliseconds)
configuration.request_timeout = 1000

# Allowlisted and Denylisted headers are case insensitive
# and allow to use _ and - as a separator, http prefixes are removed
# By default all headers are passed, but some are automatically scrubbed.
# If you need to apply an allowlist, we recommend using the minimum set of
# standard headers that we've exposed in the `DEFAULT_ALLOWLIST` constant.
# Allowlisted headers
configuration.allowlisted = DEFAULT_ALLOWLIST + ['X_HEADER']

# Denylisted headers take advantage over allowlisted elements. Note that
# some headers are always scrubbed, for security reasons.
configuration.denylisted = ['HTTP-X-header']

# Castle needs the original IP of the client, not the IP of your proxy or load balancer.
# The SDK will only trust the proxy chain as defined in the configuration.
# We try to fetch the client IP based on X-Forwarded-For or Remote-Addr headers in that order,
# but sometimes the client IP may be stored in a different header or order.
# The SDK can be configured to look for the client IP address in headers that you specify.
# If the specified header or X-Forwarded-For default contains a proxy chain with public IP addresses,
# then one of the following must be set
# 1. The trusted_proxies value must match the known proxy IP's
# 2. The trusted_proxy_depth value must be set to the number of known trusted proxies in the chain (see below)
configuration.ip_headers = []

# Additionally to make X-Forwarded-For and other headers work better discovering client ip address,
# and not the address of a reverse proxy server, you can define trusted proxies
# which will help to fetch proper ip from those headers

# In order to extract the client IP of the X-Forwarded-For header
# and not the address of a reverse proxy server, you must define all trusted public proxies
# you can achieve this by listing all the proxies ip defined by string or regular expressions
# in trusted_proxies setting
configuration.trusted_proxies = []
# or by providing number of trusted proxies used in the chain
configuration.trusted_proxy_depth = 0

# If there is no possibility to define options above and there is no other header which can have client ip
# then you may set trust_proxy_chain = true to trust all of the proxy IP's in X-Forwarded-For
configuration.trust_proxy_chain = false

# *Note: default always marked as trusty list is here: Castle::Configuration::TRUSTED_PROXIES


Here is a simple example of track event.

from castle.client import Client
from castle import events

castle = Client.from_request(request)
  'event': events.LOGIN_SUCCEEDED,
  'user_id': 'user_id'

The client will automatically configure the context for each request.


from secure_mode import signature


will create a signed user_id.

Async tracking

By default Castle sends requests synchronously. To send requests in a background worker you can generate data for a worker:

from castle.client import Client
from castle import events

context = Client.to_context(request)
options = Client.to_options({
  'event': events.LOGIN_SUCCEEDED,
  'properties': {
    'key': 'value'
  'user_traits': {
    'key': 'value'

and use it later in a way

from castle.client import Client

client = Client(context)


List of Recognized Events can be found here or in the docs.


CastleError will be thrown if the Castle API returns a 400 or a 500 level HTTP response. You can also choose to catch a more finegrained error.


Documentation and links to additional resources are available at

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