Resolution
The Pipeline script needs to use the results of one of the calls to determine the input data to the next call. This is possible pending JENKINS-26133 by writing the data to a file which is consumed by the next step.
Please note that the steps can be run on different nodes by doing the following:
def content
node {
sh 'curl -s https://server/api1/resource > .resource'
content = readFile '.resource'
}
node {
sh "curl -s https://server/api2/${content} > .resource"
// …
}