You use a PUT request to the roles resource of RestMan to add a new role assignment. There are a few steps required to gather the information needed. It is expected that the identity has already been created in the IDP.
First you need to know the id of the role. You can use:
GET 1.0/roles
but it will retrieve the entire list of roles, which can be very large if a lot of services and policies are defined. It is better to get the specific role by name:
GET 1.0/roles?name=Administrator
Extract the /l7:List/l7:Item/l7:Id field to get the ID of the role. The Administrator role ID *should* always be 0000000000000000ffffffffffffff9c.
Next retrieve the IDP ID:
GET 1.0/1.0/identityProviders
then extract the /l7:List/l7:Item/l7:Id field to get the ID of the identity provider you will use. The Internal Identity Provider ID *should* always be 0000000000000000fffffffffffffffe.
To generate the request for the PUT call, you can get the roles template by issuing a GET request to roles/{id}/assignments/template/addassignments, substituting {id} for the ID of the role:
GET 1.0/roles/0000000000000000ffffffffffffff9c/assignments/template/addassignments
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<l7:Item xmlns:l7="http://ns.l7tech.com/2010/04/gateway-management">
<l7:Name>AddAssignmentsContext Template</l7:Name>
<l7:Type>AddAssignmentsContext</l7:Type>
<l7:TimeStamp>2018-08-27T10:20:16.569-07:00</l7:TimeStamp>
<l7:Resource>
<l7:AddAssignmentsContext>
<l7:assignments>
<l7:assignment>
<l7:providerId>ProviderID</l7:providerId>
<l7:identityName>Name</l7:identityName>
<l7:entityType>User or Group</l7:entityType>
</l7:assignment>
</l7:assignments>
</l7:AddAssignmentsContext>
</l7:Resource>
</l7:Item>
Template calls always show the template as the l7:Resource content, so from that you can generate the request message for the PUT call starting at the l7:AddAssignmentsContext element. Note you will need to transfer the namespace down to the element. Once you have fleshed out the template you just PUT it to the role's assignments resource:
PUT 1.0/roles/0000000000000000ffffffffffffff9c/assignments
<l7:AddAssignmentsContext xmlns:l7="http://ns.l7tech.com/2010/04/gateway-management">
<l7:assignments>
<l7:assignment>
<l7:providerId>0000000000000000fffffffffffffffe</l7:providerId>
<l7:identityName>test</l7:identityName>
<l7:entityType>User</l7:entityType>
</l7:assignment>
</l7:assignments>
</l7:AddAssignmentsContext>
You should get a 204 "No Content" response, so don't be too surprised when the response is blank.
BTW this is basically described by the RestMan documentation if you look at the Roles resource, although some of the steps are not exactly intuitive so hopefully this response helps.