lib/omniauth/failureendpoint.rb in OmniAuth before 1.9.2 (and before 2.0) does not escape the messagekey value.
{ "binaries": [ { "binary_version": "1.3.1-1+deb9u1build0.16.04.1", "binary_name": "ruby-omniauth" } ] }
{ "binaries": [ { "binary_version": "1.6.1-2", "binary_name": "ruby-omniauth" } ] }
{ "binaries": [ { "binary_version": "1.9.0-1", "binary_name": "ruby-omniauth" } ] }
{ "binaries": [ { "binary_version": "1.9.1-1", "binary_name": "ruby-omniauth" } ] }
{ "binaries": [ { "binary_version": "2.1.1-1", "binary_name": "ruby-omniauth" } ] }
{ "binaries": [ { "binary_version": "2.1.1-4", "binary_name": "ruby-omniauth" } ] }