@startuml
actor       Browser as user
participant Proxy as proxy
participant "Captcha Provider" as captcha
participant "Backend" as backend
user -> proxy: Request /resource?foo=bar
activate proxy
proxy -> user: Redirect /{captcha_url}
deactivate proxy

user -> captcha: Submit challenge
activate captcha
captcha -> user: Pass challenge result hash
deactivate captcha
user -> proxy: Submit captcha form

activate proxy
proxy -> captcha: Validate challenge results
activate captcha
captcha -> proxy: Pass validation results
deactivate captcha
proxy -> user: Redirect /resource?foo=bar
deactivate proxy
user -> proxy: Request /resource?foo=bar
activate proxy
proxy -> backend: Request /resource?foo=bar
activate backend
backend -> proxy: Serve /resource?foo=bar
deactivate backend
proxy -> user: Serve /resource?foo=bar
deactivate proxy
@enduml