4.4 KiB
Challenges
Challenges can be transparent (not shown to user, depends on backend or other logic), non-JavaScript (challenges common browser properties), or custom JavaScript (from Proof of Work to fingerprinting or Captcha is supported)
Transparent
http
Verify incoming requests against a specified backend to allow the user through. Cookies and some other headers are passed.
For example, this allows verifying the user cookies against the backend to have the user skip all other challenges.
Example on Forgejo, checks that current user is authenticated:
http-cookie-check:
runtime: http
parameters:
http-url: http://forgejo:3000/user/stopwatches
# http-url: http://forgejo:3000/repo/search
# http-url: http://forgejo:3000/notifications/new
http-method: GET
http-cookie: i_like_gitea
http-code: 200
verify-probability: 0.1
preload-link
Requires HTTP/2+ response parsing and logic, silent challenge (does not display a challenge page).
Browsers that support 103 Early Hints are indicated to fetch a CSS resource via Link preload that solves the challenge.
The server waits until solved or defined timeout, then continues on other challenges if failed.
Example:
preload-link:
condition: '"Sec-Fetch-Mode" in headers && headers["Sec-Fetch-Mode"] == "navigate"'
runtime: "preload-link"
parameters:
preload-early-hint-deadline: 3s
dnsbl
You can configure a DNSBL (Domain Name System blocklist) to be queried.
This allows you to serve harder or different challenges to higher risk clients, or block them from specific sections.
Only rules that match a DNSBL challenge will cause a query to be sent, meaning the bulk of requests will not be sent to this service upstream.
Results will be temporarily cached.
By default, DroneBL is used.
Example challenge definition and rule:
challenges:
dnsbl:
runtime: dnsbl
parameters:
# dnsbl-host: "dnsbl.dronebl.org"
dnsbl-decay: 1h
dnsbl-timeout: 1s
rules:
# check DNSBL and serve harder challenges
- name: undesired-dnsbl
action: check
settings:
challenges: [dnsbl]
# if DNSBL fails, check additional challenges
fail: check
fail-settings:
challenges: [js-pow-sha256]
Non-JavaScript
cookie
Requires HTTP parsing and a Cookie Jar, silent challenge (does not display a challenge page unless failed).
Serves the client with a Set-Cookie that solves the challenge, and redirects it back to the same page. Browser must present the cookie to load.
Several tools implement this, but usually not mass scrapers.
header-refresh
Requires HTTP response parsing and logic, displays challenge site instantly.
Have the browser solve the challenge by following the URL listed on HTTP Refresh instantly.
meta-refresh
Requires HTTP and HTML response parsing and logic, displays challenge site instantly.
Have the browser solve the challenge by following the URL listed on HTML <meta http-equiv=refresh> tag instantly. Equivalent to above.
resource-load
Requires HTTP and HTML response parsing and logic, displays challenge site.
Servers a challenge page with a linked resource that is loaded by the browser, which solves the challenge. Page refreshes a few seconds later via Refresh.
Custom JavaScript
js-pow-sha256
Requires JavaScript and workers, displays challenge site.
Has the user solve a Proof of Work using SHA256 hashes, with configurable difficulty.
Example:
js-pow-sha256:
runtime: js
parameters:
# specifies the folder path that assets are under
# can be either embedded or external path
# defaults to name of challenge
path: "js-pow-sha256"
# needs to be under static folder
js-loader: load.mjs
# needs to be under runtime folder
wasm-runtime: runtime.wasm
wasm-runtime-settings:
difficulty: 20
verify-probability: 0.02