# HG changeset patch
# User Kim Alvefur <zash@zash.se>
# Date 1684324290 -7200
# Node ID 06640647d193f170bcfb39ca167c68d2cea8b681
# Parent  c0d62c1b4424d5b314386e50216864839c9c083b
mod_http_oauth2: Fix use of arbitrary ports in loopback redirect URIs

Per draft-ietf-oauth-v2-1-08#section-8.4.2
> The authorization server MUST allow any port to be specified at the
> time of the request for loopback IP redirect URIs, to accommodate
> clients that obtain an available ephemeral port from the operating
> system at the time of the request.

Uncertain if it should normalize the host part, but it also seems
harmless to treat IPv6 and IPv4 the same here.

One thing is that "localhost" is NOT RECOMMENDED because it can
sometimes be pointed to non-loopback interfaces via DNS or hosts file.

diff -r c0d62c1b4424 -r 06640647d193 mod_http_oauth2/mod_http_oauth2.lua
--- a/mod_http_oauth2/mod_http_oauth2.lua	Wed May 17 00:55:50 2023 +0200
+++ b/mod_http_oauth2/mod_http_oauth2.lua	Wed May 17 13:51:30 2023 +0200
@@ -236,6 +236,17 @@
 	};
 end
 
+local function normalize_loopback(uri)
+	local u = url.parse(uri);
+	if u.scheme == "http" and loopbacks:contains(u.host) then
+		u.authority = nil;
+		u.host = "::1";
+		u.port = nil;
+		return url.build(u);
+	end
+	-- else, not a valid loopback uri
+end
+
 local function get_redirect_uri(client, query_redirect_uri) -- record client, string : string
 	if not query_redirect_uri then
 		if #client.redirect_uris ~= 1 then
@@ -251,11 +262,19 @@
 			return redirect_uri
 		end
 	end
-	-- FIXME The authorization server MUST allow any port to be specified at the
-	-- time of the request for loopback IP redirect URIs, to accommodate clients
-	-- that obtain an available ephemeral port from the operating system at the
-	-- time of the request.
+	-- The authorization server MUST allow any port to be specified at the time
+	-- of the request for loopback IP redirect URIs, to accommodate clients that
+	-- obtain an available ephemeral port from the operating system at the time
+	-- of the request.
 	-- https://www.ietf.org/archive/id/draft-ietf-oauth-v2-1-08.html#section-8.4.2
+	local loopback_redirect_uri = normalize_loopback(query_redirect_uri);
+	if loopback_redirect_uri then
+		for _, redirect_uri in ipairs(client.redirect_uris) do
+			if loopback_redirect_uri == normalize_loopback(redirect_uri) then
+				return query_redirect_uri;
+			end
+		end
+	end
 end
 
 local grant_type_handlers = {};