I can create a secure, multi-tenant web app with Grails by :

• setup spring security plugin,
• setup Multi-tenant plugin (via multi-tenant install and multi-tenant-spring-security)

• update config.groovy :

  tenant { mode = "multiTenant" resolver.type = "springSecurity" }

• add : Integer userTenntId in User domain

• add a domain class for tenant Organization
• associate the tenants with Organization
• Edit BootStrap.groovy.

Everything works fine in multi-tenant mode, but how to use mode = "singleTenant" ?
This configuration sound not working :

tenant { mode = "singleTenant" resolver.type = "springSecurity" }

Edit :

I try this config :

tenant {
  mode = "singleTenant"
  resolver.type = "springSecurity"
  datasourceResolver.type = "config"

  dataSourceTenantMap {
    t1 = "jdbc:hsqldb:file:custFoo"
    t2 = "jdbc:hsqldb:file:custBar"
  }
}

But I get :

ERROR errors.GrailsExceptionResolver  - Executing action [list] of controller [org.example.TicketController]  caused exception: java.lang.StackOverflowError

and :

Caused by: java.lang.StackOverflowError
    at org.grails.multitenant.springsecurity.SpringSecurityCurrentTenant.getTenantIdFromSpringSecurity(SpringSecurityCurrentTenant.groovy:50)
    at org.grails.multitenant.springsecurity.SpringSecurityCurrentTenant.this$2$getTenantIdFromSpringSecurity(SpringSecurityCurrentTenant.groovy)
    at org.grails.multitenant.springsecurity.SpringSecurityCurrentTenant$this$2$getTenantIdFromSpringSecurity.callCurrent(Unknown Source)
    at org.grails.multitenant.springsecurity.SpringSecurityCurrentTenant.get(SpringSecurityCurrentTenant.groovy:41)
    at com.infusion.tenant.spring.TenantBeanContainer.getBean(TenantBeanContainer.java:53)
    at com.infusion.tenant.spring.TenantMethodInterceptor.invoke(TenantMethodInterceptor.java:32)
    at $Proxy14.getConnection(Unknown Source)