FortiGate authenticate with radius and local user.

[debabratamajhi]

Hello All,

I am using FortiGate 6.4.X ,Want to implement radius base authentication. I configured the Radius server and able to login through both Radius and local admin user.
Now I want prioritize the authentication method in such way .
like default authentication will be  using Radius base and if radius fail it will allow local user.

Any help much appreciated 

Thanks

[bmeta]

https://fortinetweb.s3.amazonaws.com/docs.fortinet.com/v2/attachments/2c0e7d50-6d7a-11eb-9995-00505692583a/FortiOS-6.4.5-Administration_Guide.pdf
PAGE 1648
User Groups
A user group is a list of users.
Security policies and some VPN configurations only allow access to specified user groups.
This restricted access enforces role-based access control (RBAC) to your organization's network and resources.
Users must be in a group and that group must be part of the security policy.
In most cases, FortiOS authenticates a user by requesting their username and password.
FortiOS checks local user accounts first.
Then, if it does not find a match, FortiOS checks the RADIUS, LDAP, and TACACS+ servers that belong to the user group.
Authentication succeeds when FortiOS finds a matching username and password.
If the user belongs to multiple groups on a server, FortiOS matches those groups as well.
FortiOS does not allow username overlap between RADIUS, LDAP, and TACACS+ servers.