Who Can Alter A Mapping

Now Firebird support multiple security databases, new problems arise that could not occur with a single, global security database. Clusters of databases using the same security database are effectively separated. Mappings provide the means to achieve the same effect when multiple databases are using their own security databases. Some cases require control for limited interaction between such clusters. For example:

when EXECUTE STATEMENT ON EXTERNAL DATA SOURCE requires data exchange between clusters
when server-wide SYSDBA access to databases is needed from other clusters, using services.
On Windows, due to support for Trusted User authentication: to map Windows users to a Firebird user and/or role. An example is the need for a ROLE granted to a Windows group to be assigned automatically to members of that group.

The single solution for all such cases is mapping the login information assigned to a user when it connects to a Firebird server to internal security objects in a database — CURRENT_USER and CURRENT_ROLE.

The Mapping Rule

The mapping rule consists of four pieces of information:

mapping scope — whether the mapping is local to the current database or whether its effect is to be global, affecting all databases in the cluster, including security databases
mapping name — an SQL identifier, since mappings are objects in a database, like any other
the object FROM which the mapping maps. It consists of four items:
- The authentication source
  - plugin name or
  - the product of a mapping in another database or
  - use of server-wide authentication or
  - any method
- The name of the database where authentication succeeded
- The name of the object from which mapping is performed
- The type of that name — username, role, or OS group — depending upon the plugin that added that name during authentication.
  
  Any item is accepted but only type is required.
the object TO which the mapping maps. It consists of two items:
- The name of the object TO which mapping is performed
- The type, for which only USER or ROLE is valid

`CREATE MAPPING`

Creates a mapping of a security object

Available in

DSQL

Syntax

CREATE [GLOBAL] MAPPING name
  USING
    { PLUGIN plugin_name [IN database]
    | ANY PLUGIN [IN database | SERVERWIDE]
    | MAPPING [IN database] | '*' [IN database] }
  FROM {ANY type | type from_name}
  TO {USER | ROLE} [to_name]

Table 1. `CREATE MAPPING` Statement Parameter
Parameter	Description
name	Mapping name The maximum length is 63 characters. Must be unique among all mapping names in the context (local or `GLOBAL`).
plugin_name	Authentication plugin name
database	Name of the database that authenticated against
type	The type of object to be mapped. Possible types are plugin-specific.
from_name	The name of the object to be mapped
to_name	The name of the user or role to map to

The CREATE MAPPING statement creates a mapping of security objects (e.g. users, groups, roles) of one or more authentication plugins to internal security objects — CURRENT_USER and CURRENT_ROLE.

If the GLOBAL clause is present, then the mapping will be applied not only for the current database, but for all databases in the same cluster, including security databases.

Warning

There can be global and local mappings with the same name. They are distinct objects.

Note

Global mapping works best if a Firebird 3.0 or higher version database is used as the security database. If you plan to use another database for this purpose — using your own provider, for example — then you should create a table in it named RDB$MAP, with the same structure as RDB$MAP in a Firebird 3.0 or higher database and with SYSDBA-only write access.

The USING clause describes the mapping source. It has a complex set of options:

an explicit plugin name (PLUGIN plugin_name) means it applies only for that plugin
it can use any available plugin (ANY PLUGIN); although not if the source is the product of a previous mapping
it can be made to work only with server-wide plugins (SERVERWIDE)
it can be made to work only with previous mapping results (MAPPING)
you can omit to use of a specific method by using the asterisk (*) argument
it can specify the name of the database that defined the mapping for the FROM object (IN database)

Note

This argument is not valid for mapping server-wide authentication.

The FROM clause describes the object to map. The FROM clause has a mandatory argument, the type of the object named. It has the following options:

When mapping names from plugins, type is defined by the plugin
When mapping the product of a previous mapping, type can be only USER or ROLE
If an explicit from_name is provided, it will be taken into account by this mapping
Use the ANY keyword to work with any name of the given type.

The TO clause specifies the user or role that is the result of the mapping. The to_name is optional. If it is not specified, then the original name of the mapped object will be used.

For roles, the role defined by a mapping rule is only applied when the user does not explicitly specify a role on connect. The mapped role can be assumed later in the session using SET TRUSTED ROLE, even when the mapped role is not explicitly granted to the user.

Who Can Create a Mapping

The CREATE MAPPING statement can be executed by:

Administrators
The database owner — if the mapping is local
Users with the CHANGE_MAPPING_RULES system privilege — if the mapping is local

`CREATE MAPPING` examples

Enable use of Windows trusted authentication in all databases that use the current security database:
```
CREATE GLOBAL MAPPING TRUSTED_AUTH
  USING PLUGIN WIN_SSPI
  FROM ANY USER
  TO USER;
```
Enable RDB$ADMIN access for windows admins in the current database:
```
CREATE MAPPING WIN_ADMINS
  USING PLUGIN WIN_SSPI
  FROM Predefined_Group
  DOMAIN_ANY_RID_ADMINS
  TO ROLE RDB$ADMIN;
```
Note

The group DOMAIN_ANY_RID_ADMINS does not exist in Windows, but such a name would be added by the Win_Sspi plugin to provide exact backwards compatibility.
Enable a particular user from another database to access the current database with another name:
```
CREATE MAPPING FROM_RT
  USING PLUGIN SRP IN "rt"
  FROM USER U1 TO USER U2;
```
Important

Database names or aliases will need to be enclosed in double quotes on operating systems that have case-sensitive file names.
Enable the server’s SYSDBA (from the main security database) to access the current database. (Assume that the database is using a non-default security database):
```
CREATE MAPPING DEF_SYSDBA
  USING PLUGIN SRP IN "security.db"
  FROM USER SYSDBA
  TO USER;
```
Ensure users who logged in using the legacy authentication plugin do not have too many privileges:
```
CREATE MAPPING LEGACY_2_GUEST
  USING PLUGIN legacy_auth
  FROM ANY USER
  TO USER GUEST;
```

`ALTER MAPPING`

Alters a mapping of a security object

Available in

DSQL

Syntax

ALTER [GLOBAL] MAPPING name
  USING
    { PLUGIN plugin_name [IN database]
    | ANY PLUGIN [IN database | SERVERWIDE]
    | MAPPING [IN database] | '*' [IN database] }
  FROM {ANY type | type from_name}
  TO {USER | ROLE} [to_name]

For details on the options, see [fblangref50-security-mapping-create].

The ALTER MAPPING statement allows you to modify any of the existing mapping options, but a local mapping cannot be changed to GLOBAL or vice versa.

Important

Global and local mappings of the same name are different objects.