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By default, the AppSignal integrations track request HTTP headers for web applications in supported libraries. You can set custom request headers on a transaction or span. Modifying the request headers will overwrite the data set by the AppSignal instrumentations. All request headers are filtered by our integrations before being sent to our servers.
🔐 Do not send Personal Identifiable Information (PII) to AppSignal. Filter PII (e.g., names, emails) and use an ID, hash, or pseudonymized identifier instead.

Use Link Templates to link them back in your app.
See the table below for a list of accepted value types for request headers.
LanguageAccepted header nameAccepted header value
RubyStringString
ElixirStringString
Node.jsStringString
PythonStringString
GoStringString, String slice
JavaStringString, String array
PHPStringString, String array
The below code sample shows how to set custom request headers: 
# Call `add_headers` multiple times to set more headers
Appsignal.add_headers("REQUEST_METHOD" => "GET", "REQUEST_PATH" => "/some-path")
Appsignal.add_headers("PATH_INFO" => "/a-path")
Appsignal.add_headers("PATH_INFO" => "/some-path")
# Headers:
# {
#   "REQUEST_METHOD" => "GET",
#   "REQUEST_PATH" => "/some-path",
#   "PATH_INFO" => "/some-path"
# }
For certain languages, additional setup is required. Please follow the instructions for these languages: environment

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Limitations

Only the last value for a request header is stored if the application sets a request header multiple times. For Elixir, if the helper is called multiple times, only the last set of request headers (environment) is stored.