SourceOne Email Management : Search Single sign-On Fails with an authentication error

Single sign on for SourceOne WebSearch fails with the following error:

"Unable to authorize with the web service"
 
The error "An Error has occurred" gets reported when the browser is refreshed and we see a 401 error in IIS logs:

<Date Time> <IP> GET /search/ - Port  -<IP adress> Mozilla/5.0+(Windows+NT+6.3;+Win64;+x64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/75.0.3770.100+Safari/537.36 - 401 2 5 0
<Date Time> <IP> POST /SearchWS/ExSearchWebService.asmx - port - <IP> Mozilla/4.0+(compatible;+MSIE+6.0;+MS+Web+Services+Client+Protocol+4.0.30319.42000) - 401 2 5 0
<Date Time>  <IP> POST /SearchWS/ExSearchWebService.asmx - Port <Service account Name>
<IP> Mozilla/4.0+(compatible;+MSIE+6.0;+MS+Web+Services+Client+Protocol+4.0.30319.42000) - 401 5 0 0

The issue is caused by the Allow rule under .Net Authorization for SearchWS having the incorrect service account 

• The Service account has been added with "service account" name.
• The correct configuration is "Domain\service account name"

The add rule should be created with either of the following settings :

•  The EMC SourceOne security group role by using the Specified roles or user groups entry fields.

or

• The EMC SourceOne service account user by using the Specified users entry field.

The SourceOne Service account should be configured as "Domain\ServiceAccount Name " instead of just service account name

If the configuration is not as "Domain\Service Account" SSO will fail

Single Sign On configuration for SourceOne search is explained in detail in the installation guide of SourceOne email management.