Hi, we have a service that only implement's ldap authentication. We would like to use radius. Is there a method to allow bridging from ldap to radius?

If I understand you correctly, you want Radius to use LDAP for authentication. If so, then yes: that is possible. Have a look at Freeradius which has an LDAP driver that (at least several years ago) worked flawlessly against OpenLDAP. There may be other Radius servers with similar capabilities.

-JP