Question: Title mostly says it. How can you trigger a Jenkins multibranch pipeline project build from a remote git repository?

The "Trigger builds remotely" build trigger option does not seem to work, since no tokens that you set are saved.

Answer: 
At the moment (Jenkins 2.22) the "Trigger builds remotely" build trigger option is visible in the multibranch pipeline job configuration, but does not work (if you check it and specify a token, it gets reset after saving anyway). According to [this](https://issues.jenkins-ci.org/browse/JENKINS-35310), it is intentional that the trigger cannot be set, but a bug that it appears as an option at all. 

In the same thread they explain how to trigger builds for each individual project (branch) in a multibranch pipeline project. What I needed was a dynamic setup that would work for branches created after setting up the trigger, so rather than the suggested endpoint from the thread (`/job/project-name/job-name/build`, which should have been `/job/job-name/project-name/build` , since projects are created from branches in a job), I found that the endpoint to use is `/job/job-name/build`. In order for that to work you have to create a user with an API token (go to Manage Jenkins -> Manage Users -> Gear icon -> Show API Token), and use those as username and password in your request.

The solution might be obvious for those used to working with Jenkins REST API, but when you are new to both multibranch pipeline projects and the REST API, it doesn't hurt to be explicit.
I couldn't get the API token as described in the accepted answer because there is no such link called "Manage Users" even though I log in as admin. Instead, I got the token as described in the [Jenkins Wiki](https://wiki.jenkins.io/display/JENKINS/Authenticating+scripted+clients):

> 
> The API token is available in your personal configuration page. Click
>  your name on the top right corner on every page, then click
>  "Configure" to see your API token
> 
> 
> 

Once you have the token, the following curl request will trigger a new build for a multibranch pipeline (Replace placeholders starting with `$`)

```
curl -X POST -u "$jenkins_username:$api_token" "http://$jenkins_url/job/$my-pipeline/job/$branch_name/build?token=BUILD_TOKEN"

```

**Notes**:

1. If the pipeline or branch name contains special characters, you need to encode it; for example, `/` becomes `%252F`.
2. The `token` query parameter is optional.
3. This answer has been verified in Jenkins v2.6.