You can use Subject Query Endpoint
POST https://vssps.dev.azure.com/{organization}/_apis/graph/subjectquery?api-version=6.0-preview.1
Body should look like this:
{
"query": "Term to search (e.g. Krzysztof)",
"subjectKind": [ "User" ]
}
and then you will get response like this:
{
"count": 3,
"value": [
{
"subjectKind": "user",
"metaType": "member",
"domain": "Windows Live ID",
"principalName": "mail@mail.com,
"mailAddress": "mail@mail.com",
"origin": "msa",
"originId": "0006BFFDBC3FE9A1",
"displayName": "Krzysztof Madej",
"_links": {
"self": {
"href": "https://vssps.dev.azure.com/thecodemanual/_apis/Graph/Users/msa.MDQ5MGM0N2ItODNiNC03MmEzLTk2MzgtZTJhMmNjOTY3NWQ3"
},
"memberships": {
"href": "https://vssps.dev.azure.com/thecodemanual/_apis/Graph/Memberships/msa.MDQ5MGM0N2ItODNiNC03MmEzLTk2MzgtZTJhMmNjOTY3NWQ3"
},
"membershipState": {
"href": "https://vssps.dev.azure.com/thecodemanual/_apis/Graph/MembershipStates/msa.MDQ5MGM0N2ItODNiNC03MmEzLTk2MzgtZTJhMmNjOTY3NWQ3"
},
"storageKey": {
"href": "https://vssps.dev.azure.com/thecodemanual/_apis/Graph/StorageKeys/msa.MDQ5MGM0N2ItODNiNC03MmEzLTk2MzgtZTJhMmNjOTY3NWQ3"
},
"avatar": {
"href": "https://dev.azure.com/thecodemanual/_apis/GraphProfile/MemberAvatars/msa.MDQ5MGM0N2ItODNiNC03MmEzLTk2MzgtZTJhMmNjOTY3NWQ3"
}
},
"url": "https://vssps.dev.azure.com/thecodemanual/_apis/Graph/Users/msa.MDQ5MGM0N2ItODNiNC03MmEzLTk2MzgtZTJhMmNjOTY3NWQ3",
"descriptor": "msa.MDQ5MGM0N2ItODNiNC03MmEzLTk2MzgtZTJhMmNjOTY3NWQ3"
},
as next ise originId
in reviewers
collection.