Postman pre-request script to create necessary values to make a call to Cosmos DB REST API with Authorization request headers.

postman-pre-request-script-cosmosdb.js

/**
 * This POSTMAN pre-request script help to create necessary values
 * to make a call to Cosmos DB REST API with Authorization request headers 
 * and set those headers to each request.
 * See REST API into in: https://docs.microsoft.com/en-us/rest/api/cosmos-db/
 * See access control reference on: 
 * https://docs.microsoft.com/en-us/rest/api/cosmos-db/access-control-on-cosmosdb-resources
 * Josué Martínez Buenrrostro @josuemb on twitter
 */

// Checking for mandatory collection variables need to be present in any call, those are:
// Authorization, x-ms-version, Authorization and x-ms-date.
// When Authorization and x-ms-date values are going to be filled in this script.
// See reference on: https://docs.microsoft.com/en-us/rest/api/cosmos-db/common-cosmosdb-rest-request-headers
pm.test("Check for collectionVariables", function () {
    let vars = ['authorization_type', 'authorization_version', 'authorization_signature', 'x-ms-version'];
    vars.forEach(function (item, index, array) {
        pm.expect(pm.collectionVariables.get(item), item + ' variable not set').to.not.be.undefined;
        pm.expect(pm.collectionVariables.get(item), item + ' variable not set').to.not.be.empty; 
    });    
});

// Get URL value from request.
let url = pm.request.url.toString();
//Regular expression to separate parameters in pair with resource name and resource id when resource id is optional.
let urlRegExp = /^https?:\/\/.*\.documents\.azure\.com(?::\d+)?(?:\/([^\/]+)(?:\/([^\/]+)?)?)+$/i;

// Checking for valid URL syntax.
// See: https://docs.microsoft.com/en-us/rest/api/cosmos-db/cosmosdb-resource-uri-syntax-for-rest
pm.test("Check for URL valid format", function() {
    pm.expect(url, 'URL not set').to.not.be.undefined;
    pm.expect(url, 'URL not set').to.not.be.empty;
    pm.expect(urlRegExp.test(url), 'URL does not have a valid format. See: https://docs.microsoft.com/en-us/rest/api/cosmos-db/cosmosdb-resource-uri-syntax-for-rest').to.be.true;
});

// Getting necessary values from collection variables.
// See: https://learning.postman.com/docs/sending-requests/variables/
let autorizationType = pm.collectionVariables.get('authorization_type');
let autorizationVersion = pm.collectionVariables.get('authorization_version');
let authorizationSignature = pm.collectionVariables.get('authorization_signature');
let cosmosDBApiVersion = pm.collectionVariables.get('x-ms-version')

// Decode authorization signature (it is originally base64 coded)
let key = CryptoJS.enc.Base64.parse(authorizationSignature);
// Set request date formatting as UTC
let dateUtc = new Date().toUTCString();
// Get request method (a.k.a. verb) to build text for authorization token
let verb = pm.request.method;

// Execute regular expression to extract some parts from URL.
let parsedUrl = urlRegExp.exec(url);
// Get resource type from URL
let resourceType = parsedUrl[1];
// Get resource ID from URL, if it is not present, we are getting undefined.
let resourceId = parsedUrl[2];
// Build regular expression to get all parameters from URL to build ResourceLink part.
// See "Example Encoding" in: https://docs.microsoft.com/en-us/rest/api/cosmos-db/access-control-on-cosmosdb-resources
let resourceLinkPattern = /^https?:\/\/.*\.documents\.azure\.com(?::\d+)?\/(.*)$/i;
let parsedResourceLink = resourceLinkPattern.exec(url);
// Get resource LInke from expression and in case last character is / we just drop it out.
let resourceLink = parsedResourceLink[1].charAt(parsedResourceLink[1].length-1) === "/"?
    parsedResourceLink[1].substring(parsedResourceLink[1], parsedResourceLink[1].length-1):
    parsedResourceLink[1];
// When Resource Id is present in parameters, then Resource Link is whole parameters part,
// elsewhere, then we need to drop last /resource type to
// build Resource Link.
// Example:
// for URL: https://myaccount.documents.azure.com/dbs/MyCollection/colls/
// Resource Link will be just: dbs/MyCollection
if(resourceId === undefined) { // Resource Id not provided
    // We need to cut last part to left just Resource Id
    resourceLink = resourceLink.substring(0, resourceLink.lastIndexOf('/'));
}

// Build string to be encrypted and used as signature.
// See: https://docs.microsoft.com/en-us/rest/api/cosmos-db/access-control-on-cosmosdb-resources
var text = (verb || "").toLowerCase() + "\n" +
            (resourceType || "").toLowerCase() + "\n" +
            (resourceLink || "") + "\n" +
            dateUtc.toLowerCase() + "\n\n";
// Build key to authorize request.
let signature = CryptoJS.HmacSHA256(text, key);
// Code key as base64 to be sent.
let signature_base64 = CryptoJS.enc.Base64.stringify(signature);
// Build autorization token and encode it as URI to be sent.
var authorizationToken = encodeURIComponent("type=" + autorizationType + "&ver=" + autorizationVersion + "&sig=" + signature_base64);

// Set request headers
pm.request.headers.upsert({'key': 'Accept', 'value': 'application/json'});
pm.request.headers.upsert({'key': 'x-ms-version', 'value': cosmosDBApiVersion});
pm.request.headers.upsert({'key': 'x-ms-date', 'value': dateUtc});
pm.request.headers.upsert({'key': 'Authorization', 'value': authorizationToken});