Add systemd-credential certificate loading and docs

2 files changed, 42 insertions, 13 deletions

diff --git a/README.md b/README.md
index ed1393c..2a21b42 100644
--- a/README.md
+++ b/README.md
@@ -2,12 +2,32 @@
 
 `proxy.py` is a Gemini server that proxies all content to an http or https server.
 
-## Notes
+`proxy.py` loads certificates following the structure of Apache mod_md.
+
+## Providing the certificates via systemd credentials
+
+With `/etc/systemd/system/gemini-from-http.service`:
+
+```
+[Service]
+LoadCredential=certificates:/etc/apache2/md/domains/
+ExecStart=.../proxy.py --certificates-from-credential certificates
+PrivateUsers=self
+```
+
+Systemd injects the certificates to a private path than only `proxy.py` can read.
+The injection is a one off, so you must restart the service to get updated certificates.
+
+## Providing the certificates manually
+
+To run `proxy.py` as a regular user, you can run the `package-mod-md-certs` script as root to copy the certificates to your user:
 
 ```
 su -c ./package-mod-md-certs | tar x
 ```
 
+Then you can run:
+
 ```
-./proxy.py domains/
+./proxy.py --certificates-from-path domains/
 ```
diff --git a/proxy.py b/proxy.py
index 854446b..9bdb76f 100755
--- a/proxy.py
+++ b/proxy.py
@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 import argparse
 import logging
+import os
 import pathlib
 import ssl
 import socketserver
@@ -8,7 +9,6 @@ import urllib.request
 
 
 context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
-domains_path = None
 
 class Handler(socketserver.BaseRequestHandler):
     def handle(self):
@@ -30,23 +30,32 @@ class Handler(socketserver.BaseRequestHandler):
             sock.sendall(response.encode("UTF8"))
 
 
-def sni_callback(socket: ssl.SSLSocket, server_name, _context):
-    context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
-    domain_path = domains_path / server_name
-    context.load_cert_chain(domain_path / "pubcert.pem", domain_path / "privkey.pem")
-    socket.context = context
-
-
 def main():
     logging.basicConfig(level=logging.DEBUG, format="%(asctime)s %(message)s")
     parser = argparse.ArgumentParser()
     parser.add_argument("--host", default="0.0.0.0")
     parser.add_argument("--port", type=int, default=1965)
-    parser.add_argument("domains_path", type=pathlib.Path)
+
+    group = parser.add_mutually_exclusive_group()
+    group.add_argument("--certificates-from-path", type=pathlib.Path)
+    group.add_argument("--certificates-from-credential")
     args = parser.parse_args()
 
-    global domains_path
-    domains_path = args.domains_path
+    if args.certificates_from_path:
+        def domain_to_path(server_name):
+            domain_path = args.certificates_from_path / server_name
+            return  (domain_path / "pubcert.pem" , domain_path / "privkey.pem")
+
+    if args.certificates_from_credential:
+        def domain_to_path(server_name):
+            credentials_directory = pathlib.Path(os.environ["CREDENTIALS_DIRECTORY"])
+            return (credentials_directory / f"{args.certificates_from_credential}_{server_name}_pubcert.pem", credentials_directory / f"{args.certificates_from_credential}_{server_name}_privkey.pem")
+
+    def sni_callback(socket: ssl.SSLSocket, server_name, _context):
+        context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
+        certfile, keyfile = domain_to_path(server_name)
+        context.load_cert_chain(certfile, keyfile)
+        socket.context = context
 
     context.sni_callback = sni_callback