fix: Try matching emails without plus addressing

Signed-off-by: Gustaf Räntilä <g.rantila@gmail.com>

.changeset/six-poems-press.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-auth-node': patch
+---
+
+[emailMatchingUserEntityProfileEmail resolver]: Try also matching emails with plus addressing removed.

plugins/auth-node/src/sign-in/commonSignInResolvers.ts

@@ -16,6 +16,11 @@
 
 import { createSignInResolverFactory } from './createSignInResolverFactory';
 
+// This splits an email "joe+work@acme.com" into ["joe", "+work", "@acme.com"]
+// so that we can remove the plus addressing. May output a shorter array:
+// ["joe", "@acme.com"], if no plus addressing was found.
+const reEmail = /([^@+]+)(\+[^@]+)?(@.*)/;
+
 /**
  * A collection of common sign-in resolvers that work with any auth provider.
  *
@@ -38,11 +43,28 @@ export namespace commonSignInResolvers {
             );
           }
 
-          return ctx.signInWithCatalogUser({
-            filter: {
-              'spec.profile.email': profile.email,
-            },
-          });
+          try {
+            return await ctx.signInWithCatalogUser({
+              filter: {
+                'spec.profile.email': profile.email,
+              },
+            });
+          } catch (err) {
+            // Try removing the plus addressing from the email address
+            const m = profile.email.match(reEmail);
+            if (m?.length === 4) {
+              const [_, name, _plus, domain] = m;
+              const noPlusEmail = `${name}${domain}`;
+
+              return ctx.signInWithCatalogUser({
+                filter: {
+                  'spec.profile.email': noPlusEmail,
+                },
+              });
+            }
+            // Email had no plus addressing or is missing in the catalog, forward failure
+            throw err;
+          }
         };
       },
     });