3.8 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:
mode: http
url: http://forgejo:3000/user/stopwatches
# url: http://forgejo:3000/repo/search
# url: http://forgejo:3000/notifications/new
parameters:
http-method: GET
http-cookie: i_like_gitea
http-code: 200
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:
self-preload-link:
condition: '"Sec-Fetch-Mode" in headers && headers["Sec-Fetch-Mode"] == "navigate"'
mode: "preload-link"
runtime:
# verifies that result = key
mode: "key"
probability: 0.1
parameters:
preload-early-hint-deadline: 3s
key-code: 200
key-mime: text/css
key-content: ""
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.
Example:
self-resource-load:
mode: "resource-load"
runtime:
# verifies that result = key
mode: "key"
probability: 0.1
parameters:
key-code: 200
key-mime: text/css
key-content: ""
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:
# Asset must be under challenges/{name}/static/{asset}
# Other files here will be available under that path
mode: js
asset: load.mjs
parameters:
# difficulty is number of bits that must be set to 0 from start
# Anubis challenge difficulty 5 becomes 5 * 8 = 20
difficulty: 20
runtime:
mode: wasm
# Verify must be under challenges/{name}/runtime/{asset}
asset: runtime.wasm
probability: 0.02