Anti-CLA action: what to do when you encounter a CLA

Signal Messenger is another large project that requires a CLA, featuring this clause:

  1. Grant of Copyright License. Subject to the terms and conditions of this Agreement, You hereby grant to Open Whisper Systems and to recipients of software distributed by Signal Messenger a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, and distribute Your Contributions and such derivative works, as well as the right to sublicense and have sublicensed all of the foregoing rights, through multiple tiers of sublicensees, provided that in all cases, Signal Messenger will make Your Contributions available under an OSI-approved open source license.