We have the same requirement, business case is following:

• in multibranch pipeline we want to run the build for every branch but
• deployment should be done only for the master- or hotfix-branches
• after manual confirmation
• in other branches the deployment should be skipped without interaction

We have the same requirement:

• run a stage with input only for specific branches

I found a workaround, just put your input directive inside the steps one like that

stage('Production Deploy') {
    agent { label 'linux' }
    when {
        branch "master"
    }
    steps {
        input { message 'Deploy to Production?' }
        echo 'Deploying to Production ... '
    }             
 }

This workaround blocks an executor for the time waiting for input. Following is wanted (as described in https://jenkins.io/blog/2018/04/09/whats-in-declarative/)

pipeline {
    agent none // no executor is blocked 
    stages {
        stage('Production Deploy') {
            when {
                branch 'master'
                // beforeInput: true
            }
            input { 
                message 'Deploy to Production?' // For this input can be waited several days
            }
            agent any // From here on for executing the steps an executor is needed
            steps {
                echo 'Deploying to Production ... '
            }
        }
    }
}

This’ll be in 1.3.3

Looks good!

Q: Can I, and if so how can I make the result of the captured input (the approver) available in a variable?

Thanks, works as requested.

Bulk closing resolved issues.

Just a warning, the beforeInput is not documented in the article nor in the snippet generator. I just faced this and the only solution is in Torsten's comment.