The project is open to contributions. Contributing is done by opening GitHub issues followed by Pull Requests.
The project uses the Apache 2.0 license. The license tells you what rights you have that are provided by the copyright holder. It is important that the contributor fully understands what rights they are licensing and agrees to them. Sometimes the copyright holder isn't the contributor, such as when the contributor is doing work on behalf of a company.
To make a good faith effort to ensure these criteria are met, the project requires the Developer Certificate of Origin (DCO) process to be followed.
The DCO is an attestation attached to every contribution made by every developer. In the commit message of the contribution, the developer simply adds a Signed-off-by statement and thereby agrees to the DCO, which you can find below or at http://developercertificate.org/.
Developer's Certificate of Origin 1.1
By making a contribution to this project, I certify that:
(a) The contribution was created in whole or in part by me and I
have the right to submit it under the open source license
indicated in the file; or
(b) The contribution is based upon previous work that, to the best
of my knowledge, is covered under an appropriate open source
license and I have the right under that license to submit that
work with modifications, whether created in whole or in part
by me, under the same open source license (unless I am
permitted to submit under a different license), as indicated
in the file; or
(c) The contribution was provided directly to me by some other
person who certified (a), (b) or (c) and I have not modified
it.
(d) I understand and agree that this project and the contribution
are public and that a record of the contribution (including all
personal information I submit with it, including my sign-off) is
maintained indefinitely and may be redistributed consistent with
this project or the open source license(s) involved.
The DCO requires a sign-off message in the following format appear on each commit in the pull request:
Signed-off-by: Legal Name <legal.name@company.com>
The DCO text can either be manually added to your commit body, or you can add either -s or --signoff to your usual git commit commands. If you are using the GitHub UI to make a change you can add the sign-off message directly to the commit message when creating the pull request. If you forget to add the sign-off you can also amend a previous commit with the sign-off by running git commit --amend -s. If you've pushed your changes to GitHub already you'll need to force push your branch after this with git push -f.