Postman: Set a request header from the output of a program - postman

Question

I need to make requests to an API that accepts authentication tokens and I want to be able to use a dynamically generated token by running cmd.exe /c GenerateToken.bat instead of having to run my program and then manually paste the value in Postman every time.
I imagine something that looks like this:
How can I set the value of a HTTP header to contain the stdout output of a program or a batch file?

Answer 1

Short answer is, you can't. This is deliberate, both pre-request and test scripts (the only way, other than a collection runner, to make your environment dynamic) run in the postman sandbox, which has limited functionality.
More information of what is available is in the postman-sandbox Github repository page and in postman docs (scroll to the bottom to see what libraries you can import)
You do have a few options, as described in comments - postman allows sending requests and parsing the response in scripts, so you can automate this way. You do need a server to handle the requests and execute your script (simplest option is probably a small server suporting CGI - I won't detail it here as I feel it's too big of a scope for this answer. Other options are also available, such as a small PHP or Node server)
Once you do have a server, the pre-request script is very simple:
const requestOptions = {
url: `your_server_endpoint`,
method: 'GET'
}
pm.sendRequest(requestOptions, function (err, res) {
if (err) {
throw new Error(err);
} else if (res.code != 200) {
throw new Error(`Non-200 response when fetching token: ${res.code} ${res.status}`);
} else {
var token = res.text();
pm.environment.set("my_token", token);
}
});
You can then set the header as {{my_token}} in the "Headers" tab, and it will be updated once the script runs.

Answer 2

You can do something similar to this from Pre-request Scripts at the collection level.
This is available in postman for 9 different authorization and authentication methods.
this is a sample code taken from this article, that show how to do this in Pre-request Scripts for OAuth2
// Refresh the OAuth token if necessary
var tokenDate = new Date(2010,1,1);
var tokenTimestamp = pm.environment.get("OAuth_Timestamp");
if(tokenTimestamp){
tokenDate = Date.parse(tokenTimestamp);
}
var expiresInTime = pm.environment.get("ExpiresInTime");
if(!expiresInTime){
expiresInTime = 300000; // Set default expiration time to 5 minutes
}
if((new Date() - tokenDate) >= expiresInTime)
{
pm.sendRequest({
url: pm.variables.get("Auth_Url"),
method: 'POST',
header: {
'Accept': 'application/json',
'Content-Type': 'application/x-www-form-urlencoded',
'Authorization': pm.variables.get("Basic_Auth")
}
}, function (err, res) {
pm.environment.set("OAuth_Token", res.json().access_token);
pm.environment.set("OAuth_Timestamp", new Date());
// Set the ExpiresInTime variable to the time given in the response if it exists
if(res.json().expires_in){
expiresInTime = res.json().expires_in * 1000;
}
pm.environment.set("ExpiresInTime", expiresInTime);
});
}