Process api to find Get security roles by groups

You can use the IGroupRoleMembers InProcess API:
community.telligent.com/.../grouprolemembers-in-process-api-service

You need to implement ISearchableContentType in your custom application, so when it's get called on index it will have list of all searchable content types. One of these types will be the group content type. you calli its own GetViewSecurityRoles passing the group's container id you want to get list of roles from.