mobilizon/lib/service/http_signatures/http_signatures.ex

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# https://tools.ietf.org/html/draft-cavage-http-signatures-08
defmodule Eventos.Service.HTTPSignatures do
alias Eventos.Actors.Actor
alias Eventos.Service.ActivityPub
require Logger
def split_signature(sig) do
default = %{"headers" => "date"}
sig =
sig
|> String.trim()
|> String.split(",")
|> Enum.reduce(default, fn part, acc ->
[key | rest] = String.split(part, "=")
value = Enum.join(rest, "=")
Map.put(acc, key, String.trim(value, "\""))
end)
Map.put(sig, "headers", String.split(sig["headers"], ~r/\s/))
end
def validate(headers, signature, public_key) do
sigstring = build_signing_string(headers, signature["headers"])
Logger.debug("Signature: #{signature["signature"]}")
Logger.debug("Sigstring: #{sigstring}")
{:ok, sig} = Base.decode64(signature["signature"])
:public_key.verify(sigstring, :sha256, sig, public_key)
end
def validate_conn(conn) do
# TODO: How to get the right key and see if it is actually valid for that request.
# For now, fetch the key for the actor.
with actor_id <- conn.params["actor"],
{:ok, public_key_code} <- Actor.get_public_key_for_url(actor_id),
[public_key] = :public_key.pem_decode(public_key_code),
public_key = :public_key.pem_entry_decode(public_key) do
if validate_conn(conn, public_key) do
true
else
Logger.info("Could not validate request, re-fetching user and trying one more time")
# Fetch user anew and try one more time
with actor_id <- conn.params["actor"],
{:ok, _actor} <- ActivityPub.make_actor_from_url(actor_id),
{:ok, public_key_code} <- Actor.get_public_key_for_url(actor_id),
[public_key] = :public_key.pem_decode(public_key_code),
public_key = :public_key.pem_entry_decode(public_key) do
validate_conn(conn, public_key)
end
end
else
e ->
Logger.debug("Could not found url for actor!")
Logger.debug(inspect e)
false
end
end
def validate_conn(conn, public_key) do
headers = Enum.into(conn.req_headers, %{})
[host_without_port, _] = String.split(headers["host"], ":")
headers = Map.put(headers, "host", host_without_port)
signature = split_signature(headers["signature"])
validate(headers, signature, public_key)
end
def build_signing_string(headers, used_headers) do
used_headers
|> Enum.map(fn header -> "#{header}: #{headers[header]}" end)
|> Enum.join("\n")
end
def sign(actor, headers) do
with {:ok, private_key_code} = Actor.get_private_key_for_actor(actor),
[private_key] = :public_key.pem_decode(private_key_code),
private_key = :public_key.pem_entry_decode(private_key) do
sigstring = build_signing_string(headers, Map.keys(headers))
signature =
:public_key.sign(sigstring, :sha256, private_key)
|> Base.encode64()
[
keyId: actor.url <> "#main-key",
algorithm: "rsa-sha256",
headers: Map.keys(headers) |> Enum.join(" "),
signature: signature
]
|> Enum.map(fn {k, v} -> "#{k}=\"#{v}\"" end)
|> Enum.join(",")
end
end
end