akkoma/lib/pleroma/web/http_signatures/http_signatures.ex

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# https://tools.ietf.org/html/draft-cavage-http-signatures-08
defmodule Pleroma.Web.HTTPSignatures do
alias Pleroma.User
alias Pleroma.Web.ActivityPub.Utils
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alias Pleroma.Web.ActivityPub.ActivityPub
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require Logger
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def split_signature(sig) do
default = %{"headers" => "date"}
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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/))
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end
def validate(headers, signature, public_key) do
sigstring = build_signing_string(headers, signature["headers"])
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Logger.debug("Signature: #{signature["signature"]}")
Logger.debug("Sigstring: #{sigstring}")
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{: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.
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with actor_id <- Utils.get_ap_id(conn.params["actor"]),
{:ok, public_key} <- User.get_public_key_for_ap_id(actor_id) do
if validate_conn(conn, public_key) do
true
else
Logger.debug("Could not validate, re-fetching user and trying one more time")
# Fetch user anew and try one more time
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with actor_id <- Utils.get_ap_id(conn.params["actor"]),
{:ok, _user} <- ActivityPub.make_user_from_ap_id(actor_id),
{:ok, public_key} <- User.get_public_key_for_ap_id(actor_id) do
validate_conn(conn, public_key)
end
end
else
_e ->
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Logger.debug("Could not public key!")
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false
end
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end
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def validate_conn(conn, public_key) do
headers = Enum.into(conn.req_headers, %{})
signature = split_signature(headers["signature"])
validate(headers, signature, public_key)
end
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def build_signing_string(headers, used_headers) do
used_headers
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|> Enum.map(fn header -> "#{header}: #{headers[header]}" end)
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|> Enum.join("\n")
end
def sign(user, headers) do
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with {:ok, %{info: %{keys: keys}}} <- Pleroma.Web.WebFinger.ensure_keys_present(user),
{:ok, private_key, _} = Pleroma.Web.Salmon.keys_from_pem(keys) do
sigstring = build_signing_string(headers, Map.keys(headers))
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signature =
:public_key.sign(sigstring, :sha256, private_key)
|> Base.encode64()
[
keyId: user.ap_id <> "#main-key",
algorithm: "rsa-sha256",
headers: Map.keys(headers) |> Enum.join(" "),
signature: signature
]
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|> Enum.map(fn {k, v} -> "#{k}=\"#{v}\"" end)
|> Enum.join(",")
end
end
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end