Using references to authorize access on objects

A reference can be used to authorize access on objects to a stored procedure, application, or class instance that does not have access to those objects by default.

Introduction

A reference is a string that can be used as an identifier. The identifier resolves to the object being referenced.

A reference encapsulates the following:

  • The object name.

  • The active role used to create the object reference and any active secondary role(s) if applicable.

  • The privilege(s) on the object that are specified when the reference is created.

Some scenarios where a reference might be required include:

  • An owner’s rights stored procedure requires access to insert data in a table owned by a different role.

  • An application performs data analytics and requires read access to data in tables.

  • An instance of the SNOWFLAKE.ML.ANOMALY_DETECTION class requires read access to a view for training the anomaly detection ML model.

Objects identified by name

A reference identifies an object by name. This means if an object is renamed after a reference is created, the reference is invalid. However, if a new object with the same name is created, the reference might be valid. For example, a role my_role creates a reference my_ref1 for table my_table1 with the SELECT privilege. After the reference is created, table my_table1 is dropped and a new table named my_table1 is created. The reference my_ref1 identifies a table with the name my_table1. In this case, it identifies the new table my_table1.

If the role used to create the reference, and the privilege(s) granted on my_table1 are still valid, access to the new my_table1 is authorized when using the reference.

If the role and privilege(s) encapsulated in the reference are no longer valid, access to table my_table1 cannot be authorized and a new reference must be created for the new table.

Privileges verified at execution time

The privileges granted to the role that created the reference are verified at the time the reference is used. For example, a role my_role creates a reference to a table t1 with the SELECT privilege. If my_role is dropped or the SELECT privilege on table t1 is revoked from my_role, the privileges encapsulated in the reference are no longer valid. When the reference is passed to a stored procedure that requires the SELECT privilege on the table, the stored procedure fails with a permissions error.

Types of references and reference lifespan

The lifespan of a reference can be specified at creation time.

  • A transient reference has a limited lifespan, either for the duration of the call in which the reference is passed, or for the duration of the session.

  • A persistent reference has an unlimited lifespan. The reference remains valid until the object it references is dropped, the reference is unset, or the reference becomes invalid.

    For examples of unsetting references, see Unset a persistent reference for an application.

    A reference can become invalid for any of the following reasons:

    • The object it references is renamed.

    • The role that created the reference is dropped.

    • The role that created the reference no longer has privileges on the object.

    For more information, see Objects identified by name and Privileges verified at execution time.

References for owner’s rights stored procedures

An owner’s rights stored procedure executes with the privileges of the owner rather than the privileges of the caller who executes the stored procedure. In order to perform actions on a table, view, or function that the caller has privileges to access, the caller must pass a reference to the table, view, or function. The reference enables the stored procedure to perform actions on the object that the reference identifies with the privileges of the creator of the reference (in this case, the caller).

References for applications and classes

By design, applications and classes do not have access to objects in the account where the application is installed or an instance of a class is created. Users can authorize access on objects to an application or class instance by creating a reference.

Providers and consumers of applications and classes

A provider creates an application and a consumer installs and uses an application in the consumer account. In the case of Snowflake Classes, Snowflake is the provider, and a user with a Snowflake account who creates an instance of a class is the consumer.

Providers can create applications and classes that request and use references in their code. For more information, see References for providers.

Consumers can create and pass references to applications that they install in their account or to instances of Snowflake classes. For more information, see References for consumers.

Supported targets for references

The targets for a reference can be an object or a query. If the target of the reference is an object, privilege(s) on the object are required for the reference.

Supported object types and privileges for references

The following table lists the object types that a reference can include, the type of reference that can be created, and the privileges allowed for each object:

Object Type

Transient

Persistent

Privileges Allowed

Default Privilege

DATABASE

APPLYBUDGET

SCHEMA

APPLYBUDGET

TABLE

APPLYBUDGET

SELECT, INSERT, UPDATE, DELETE, TRUNCATE, REFERENCES

SELECT

VIEW

SELECT, REFERENCES

SELECT

MATERIALIZED VIEW

APPLYBUDGET

EXTERNAL TABLE

SELECT, REFERENCES

SELECT

PIPE

APPLYBUDGET

APPLYBUDGET

TASK

APPLYBUDGET

APPLYBUDGET

FUNCTION

USAGE

USAGE

PROCEDURE

USAGE

USAGE

WAREHOUSE

APPLYBUDGET

MODIFY, MONITOR, OPERATE, USAGE

USAGE

API INTEGRATION

USAGE

USAGE

Query references

A query reference is a type of transient reference. It references a SELECT statement that can be used in the FROM clause of another SQL statement in a stored procedure. You can create a query reference by using the SYSTEM$QUERY_REFERENCE function.

For more information, see Using Query References.

References for providers

You can create applications as a provider by using the Snowflake Native App Framework. For detailed information on requesting references from a consumer of your application, see Requesting References and Object-level Privileges from Consumers.

References for consumers

You can create a reference by using the SYSTEM$REFERENCE function. You can pass the string identifier that the function returns to a stored procedure, application, or class instance. Alternatively, you can pass in the statement that creates the reference in place of the string identifier.

Examples

Create a transient reference with session scope to table t1 with the SELECT privilege:

SELECT SYSTEM$REFERENCE('TABLE', 't1', 'SESSION', 'SELECT');
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To create a reference to the same table for the lifetime of the scope in which it is referenced (for example, if you pass it to a stored procedure, its lifetime would be that of the outermost block of the stored procedure), execute the following statement:

SELECT SYSTEM$REFERENCE('TABLE', 't1', 'CALL', 'SELECT');
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Create a persistent reference to a table t1 with the INSERT privilege to pass to an application:

SELECT SYSTEM$REFERENCE('TABLE', 't1', 'PERSISTENT', 'INSERT');
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Create a query reference to pass to a stored procedure. The lifetime of this transient reference is for the outermost block of the stored procedure to which you pass the reference to:

SELECT SYSTEM$QUERY_REFERENCE('SELECT id FROM my_table', FALSE);
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For additional examples:

Unset a persistent reference for an application

An application or a class that requires a persistent reference will also provide a method to unset the reference. Method names can vary by implementation.

Alternatively, you can unset references by using an ALTER APPLICATION … UNSET REFERENCES statement.

  1. You can use the SHOW REFERENCES command to view all references, including references that have been set for an application.

    For example, to view references for application my_app:

    SHOW REFERENCES IN APPLICATION my_app;
    
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  2. You can unset any references that have been set for the application by using the ALTER APPLICATION command.

    For example, to unset the reference named table_to_read in application my_app:

    ALTER APPLICATION my_app UNSET REFERENCES('table_to_read');
    
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    For example, to unset all references in application my_app:

    ALTER APPLICATION my_app UNSET REFERENCES;
    
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Considerations when Using References

  • If an object that is associated with a reference is renamed (or reparented), the reference is no longer valid.

    If a new object is created with the same name, and if the roles encoded in the reference association have the relevant privileges on the new object, the reference remains valid. Otherwise it fails with a permissions error.

  • If an object is swapped, and the roles encoded in the reference association have the relevant privileges on the new object that now has the swapped name, the reference remains valid. Otherwise it fails with a permissions error.

  • Object drop and undrop:

    • If an object that is associated with a reference is dropped, the reference association becomes invalid.

    • If the object is undropped, the reference association becomes valid again.

  • Cloning

    You can clone a class instance, or its parent database or schema, that uses references to objects in your account.

    • If the reference object is referenced with a fully qualified name, the instance clone refers to the original object.

    • If the referenced object is referenced with a partially qualified or unqualified name, the instance clone might refer to the clone object, the original object, or to no real object depending on the cloning boundary.

  • Replication is supported for an application or a database containing a class instance that uses a reference to objects in the consumer account.

    References function correctly in the target account as long as the following objects are replicated:

    • Application or class instance.

    • Referenced object.

    • Role that created the reference.

    These objects can be replicated in different replication or failover groups. Once all objects are replicated, the reference is usable.

For providers of Snowflake Native App Framework applications, see also Considerations when Using References.

Monitoring usage of references

You can view references requested by an application by using the SHOW REFERENCES command. If you have set any references for an application, the output will include information about the object, database, schema, and the identifer for each reference.

For example, to view references in application my_app:

SHOW REFERENCES IN APPLICATION my_app;
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