{
	"wonum": "54321",
	"description": "Demo Work Order",
	"siteid": "BEDFORD"
}​

Will create a new work order with the specified work order number.  Be aware that it is your responsibility to check that that work order number has not been used previously otherwise you will get the following error.

BMXAA4129E - The record for Site=BEDFORD, Work Order=54321 already exists. Ensure that the key value for the given record is unique.

If you have custom logic you want to apply you can do so using the integration pipeline Automation Scripts. 

You can do what Steven suggested, but note that he is using the getSystemUserInfo() method to get the system user to create the work order, which means that your work order will be created as the system user and not the actual user that is performing the action.  This may impact other conditional expression behavior and bypass any security constraints you have in place.

Also, since the system user never logs out you need to be very careful to close any MboSets opened by that user otherwise they will stay in memory until server restarts, in other words you will create a memory leak.

Thanks again to Steven and Jason for your input.

I plan to pursue the OOB box option that you mentioned: "Create a WO using an object structure" ...aka... "MXWO integration object".

On a side note, I did end up pursuing the custom script option, just as a professional development exercise. It was a relatively simple example where I could learn a bit about automation scripting.

Again, I'm planning to switch to the OOB method, but for now, here's the code I came up with:

I would be happy to hear about any flaws in the script -- or improvements that could be made (knowing full-well that this is not the preferred method).

#Stack Exchange Code Review: Create or update record via HTTP request
#https://codereview.stackexchange.com/questions/245073/part-2-create-or-update-record-via-http-request

from psdi.mbo import SqlFormat
from psdi.server import MXServer
from psdi.mbo import MboSet

IGNORE_RULES = 2L

paramdict = {
    p[2:]: request.getQueryParam(p)
    for p in request.getQueryParams()
    if p.startswith('f_')
}
woset = MXServer.getMXServer().getMboSet("workorder",request.getUserInfo())

try:
    #Prevents SQL injection
    sqf = SqlFormat("wonum=:1")
    sqf.setObject(1,"WORKORDER","WONUM",request.getQueryParam("f_wonum"))

    woset.setWhere(sqf.format())
    woset.reset()
    woMbo = woset.moveFirst()

    if woMbo is None:
        woMbo=woset.add()
        verb = 'Created'
    else:
        verb = 'Updated'

    for k,v in paramdict.items():
        woMbo.setValue(k,v,IGNORE_RULES)
    resp = verb + ' workorder ' + request.getQueryParam("f_wonum")
    woset.save()
    woset.clear()
finally:
    woset.close()

responseBody = resp

{	"wonum": "54321",	"description": "Demo Work Order",	"siteid": "BEDFORD"}​

BMXAA4129E - The record for Site=BEDFORD, Work Order=54321 already exists. Ensure that the key value for the given record is unique.