Inherit email link addresses from hosting and proxy settings

backend/app/services/public_urls.py

@@ -0,0 +1,29 @@
+"""Configured public email links, independent of request Host/forwarded headers."""
+from urllib.parse import urlsplit
+from ..runtime import get_runtime_settings
+
+
+def valid_public_url(value):
+    value = str(value or '').strip().rstrip('/')
+    try:
+        parsed = urlsplit(value)
+        if (parsed.scheme in {'http', 'https'} and parsed.hostname
+                and not (parsed.username or parsed.password or parsed.query or parsed.fragment)
+                and (parsed.port is None or parsed.port > 0)
+                and not any(c.isspace() or ord(c) < 33 or c in '<>"\\' for c in value)):
+            return value
+    except ValueError:
+        pass
+    return ''
+
+
+def magent_public_url(legacy_url=''):
+    runtime = get_runtime_settings()
+    proxy = getattr(runtime, 'magent_proxy_base_url', None)
+    application = getattr(runtime, 'magent_application_url', None)
+    if getattr(runtime, 'magent_proxy_enabled', False) and str(proxy or '').strip():
+        return valid_public_url(proxy)
+    if str(application or '').strip():
+        return valid_public_url(application)
+    # Preserve pre-existing installations until Hosting & proxy has been configured.
+    return valid_public_url(legacy_url)