This is a simple example of how to use STS.getFederationToken and its result to perform actions with the new credentials, in this case S3.putObject

STS_FederationToken_nodejs

 var aws = require('aws-sdk')

    aws.config.update({accessKeyId: nconf.get('AWS_KEY'),
        secretAccessKey: nconf.get('AWS_SECRET')});

    var STS = new aws.STS({apiVersion: '2011-06-15'});

    var tempCred = STS.getFederationToken(
        {'Name': token, 'Policy': JSON.stringify(policy), 'DurationSeconds': 90000},
        function (err, data) {
            if (err) {
                return callback(err, null);
            }
            callback(null, data);
        });

    var s3 = new aws.S3({
        accessKeyId: tempCred.Credentials.AccessKeyId,
        secretAccessKey: tempCred.Credentials.SecretAccessKey,
        sessionToken: tempCred.Credentials.SessionToken

//        credentials : tempCred.Credentials // Didn't work, not sure why
    });
    s3.putObject({Bucket: nconf.get('AWS_BUCKET'),
        Body: 'Hello Stranger, I\'m temp ' + Date.now(),
        Key: nconf.get('BUCKET_DIR') + Date.now() + ".txt",
        ACL: 'public-read'
    }, function (err, data) {
        if (!err)
            console.log("Success, file saved")

        console.log(err || data)

    });