FEATURE: when suggesting usernames skip input that consist entirely of disallowed characters (#59)

Starting from https://github.com/discourse/discourse/commit/c2022521906b3c44a8a21e8eb2527c8650e06a18 we can pass to `UsernameSuggester` an array of inputs parameters and it'll be skipping invalid items and trying next ones.

.discourse-compatibility

+2.8.0.beta9: 851f6cebe3fdd48019660b236a447abb6ddf9c89
 2.8.0.beta8: 8002759dacc3c71ecf06fd33f112c84b14b6a59a
 2.8.0.beta5: c08ae1e0d301a5f0d264930fa068cdbeb5735ecd
 2.7.8: c08ae1e0d301a5f0d264930fa068cdbeb5735ecd

lib/saml_authenticator.rb

@@ -204,7 +204,7 @@ class SamlAuthenticator < ::Auth::OAuth2Authenticator
       user_params = {
         primary_email: UserEmail.new(email: try_email, primary: true),
         name: try_name || User.suggest_name(try_username || try_email),
-        username: UserNameSuggester.suggest(try_username || try_name || try_email || uid),
+        username: UserNameSuggester.suggest(try_username, try_name, try_email, uid),
         active: true
       }
 

spec/saml_authenticator_spec.rb

@@ -172,6 +172,27 @@ describe SamlAuthenticator do
       expect(result.user.id).to eq(Oauth2UserInfo.find_by(uid: @uid, provider: @authenticator.name).user_id)
     end
 
+    it 'ignores invalid input when automatically creating new account' do
+      SiteSetting.saml_auto_create_account = true
+      SiteSetting.unicode_usernames = false
+
+      nickname = "άκυρος"
+      name = "άκυρος"
+      email = "johndoe@example.com"
+
+      hash = OmniAuth::AuthHash.new(
+        uid: @uid,
+        info: {
+          name: name,
+          nickname: nickname,
+          email: email
+        }
+      )
+
+      result = @authenticator.after_authenticate(hash)
+      expect(result.user.username).to eq("johndoe")
+    end
+
     describe "username" do
       let(:name) { "John Doe" }
       let(:email) { "johndoe@example.com" }