Hello Mathanprasath,
The link above is to the OTK 3.4 documentation. OTK 3.4 only supports Gateway 9.1.
If you are running Gateway 9.0, you need to install the earlier OTK 3.3 version. You install the OAuth Solution Kit that contains policies, endpoints and assertions that create the OAuth Toolkit (OTK).
Installation instructions are here: Installation Workflow - CA API Management OAuth Toolkit - 3.3 - CA Technologies Documentation
After installation, the token issuing endpoints are created. You can call /auth/oauth/v2/authorize or /auth/oauth/v2/token depending on your grant type.
See more information:OAuth Request Scenarios - CA API Management OAuth Toolkit - 3.3 - CA Technologies Documentation
Hope that helps.
Simon