From 42a8e81370855a2c612f2acfd1c0648329a12aff Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Thu, 21 Jan 2021 13:20:58 +0000
Subject: [PATCH] Add a check for duplicate IdP ids (#9184)

---
 changelog.d/9184.misc         |  1 +
 synapse/config/oidc_config.py | 11 +++++++++++
 2 files changed, 12 insertions(+)
 create mode 100644 changelog.d/9184.misc

diff --git a/changelog.d/9184.misc b/changelog.d/9184.misc
new file mode 100644
index 000000000000..70da3d6cf59c
--- /dev/null
+++ b/changelog.d/9184.misc
@@ -0,0 +1 @@
+Emit an error at startup if different Identity Providers are configured with the same `idp_id`.
diff --git a/synapse/config/oidc_config.py b/synapse/config/oidc_config.py
index d58a83be7fea..bfeceeed18f2 100644
--- a/synapse/config/oidc_config.py
+++ b/synapse/config/oidc_config.py
@@ -15,6 +15,7 @@
 # limitations under the License.
 
 import string
+from collections import Counter
 from typing import Iterable, Optional, Tuple, Type
 
 import attr
@@ -43,6 +44,16 @@ def read_config(self, config, **kwargs):
         except DependencyException as e:
             raise ConfigError(e.message) from e
 
+        # check we don't have any duplicate idp_ids now. (The SSO handler will also
+        # check for duplicates when the REST listeners get registered, but that happens
+        # after synapse has forked so doesn't give nice errors.)
+        c = Counter([i.idp_id for i in self.oidc_providers])
+        for idp_id, count in c.items():
+            if count > 1:
+                raise ConfigError(
+                    "Multiple OIDC providers have the idp_id %r." % idp_id
+                )
+
         public_baseurl = self.public_baseurl
         self.oidc_callback_url = public_baseurl + "_synapse/oidc/callback"