Set group owner using REST API

Question

I'm trying to use the REST API to set the owner of a SharePoint group. I can successfully create the group using REST, but I can't change the owner. I've tried the following.
1 - Specifying a group owner while creating the group
Endpoint: .../_api/web/sitegroups
Method: POST
Headers:
Content-Type: application/json; odata=verbose
Body:
{ '__metadata': { 'type': 'SP.Group' }, 'Title': '<title>', 'Description': '<description>', 'Owner': { '__metadata': { 'type': 'SP.Principal' }, 'Title': '<owner_title>'}}
This returns a 500 error: "The specified name is already in use. Please try again with a new name". In other words, the owner title I specified already exists, which is correct - I'm trying to make an existing principal the owner of the new group.
2 - Merging a new group owner into an existing group
Endpoint: .../_api/web/sitegroups(<group_id>)
Method: POST
Headers:
Content-Type: application/json; odata=verbose
X-HTTP-Method: MERGE
Body:
{ '__metadata': { 'type': 'SP.Group' }, 'Owner': { '__metadata': { 'type': 'SP.Principal' }, 'Title': '<owner_title>'}}
This returns a 500 error with a Microsoft.SharePoint.SPException: "Exception from HRESULT: 0x80131904". The trace logs don't shed any light on it.
3 - Using the owner endpoint directly
Endpoint: .../_api/web/sitegroups(<group_id>)/owner
Method: POST
Headers:
Content-Type: application/json; odata=verbose
X-HTTP-Method: PUT
Body:
{ '__metadata': { 'type': 'SP.Principal' }, 'Title': '<owner_title>'}
This throws various 400 errors. If the current owner of the group is a user, I get the error "The required property 'Email' does not exist in the message" - i.e. it wants SP.User properties. If the current owner of the group is another group, I get
the error "The required property 'AllowMembersEditMembership' does not exist in the message." - i.e. it wants SP.Group properties.
I've tried various adaptations of the three approaches above, such as specifying additional SP.Principal properties or passing SP.User or SP.Group objects instead, but with no success. Any ideas?

Answer 1

As we chatted on email.  There doesn't seem to be any combo that will set the owner.  Only way to do it is to use the CSOM XML method and post to client.svc\ProcessQuery:
POST
http://weburl/_vti_bin/client.svc/ProcessQuery HTTP/1.1
X-RequestDigest: 0xAE382F0A8F11688BA9BE66739F84443892CE5E5452BA3E2622F6013D9D97EA8A8D9476463EDC503F700EB24F45024150D0DEEB2F40B160CD88BA7C7B4769BECD,15 Jan 2014 00:11:02 -0000Content-Type: text/xml
Host:
www.sanspug.org
Cookie: FedAuth=blah
Content-Length: 612
Expect: 100-continue
Accept-Encoding: gzip, deflate
XML body is:
<Request AddExpandoFieldTypeSuffix="true" SchemaVersion="15.0.0.0" LibraryVersion="15.0.0.0" ApplicationName=".NET Library" xmlns="http://schemas.microsoft.com/sharepoint/clientquery/2009">
<Actions>
<SetProperty Id="45" ObjectPathId="32" Name="Owner">
<Parameter ObjectPathId="33" />
</SetProperty>
<Method Name="Update" Id="46" ObjectPathId="32" />
</Actions>
<ObjectPaths>
<Identity Id="32" Name="740c6a0b-85e2-48a0-a494-e0f1759d4aa7:site:a1452dcc-8fc4-4631-8ada-97cb204810f1:g:9" />
<Identity Id="33" Name="740c6a0b-85e2-48a0-a494-e0f1759d4aa7:site:a1452dcc-8fc4-4631-8ada-97cb204810f1:g:7" />
</ObjectPaths></Request>
The ids are randomly generated and can be anything you want, as long as they correlate (setproperty and method objectpathid is the object you are updating).  The most important part is the
“Name” parts. The first part is the typeid of the object (in this case is means SPGroup), the second part as you can see if the site guid id.  The response does in fact return json if you tell it too:
Chris Givens CEO, Architecting Connected Systems
Blog Twitter