»MSSQL Secrets Engine

The MSSQL secrets engine for Vault generates database credentials dynamically based on configured roles. This means that services that need to access a database no longer need to hardcode credentials: they can request them from Vault, and use Vault's leasing mechanism to more easily roll keys.

Additionally, it introduces a new ability: with every service accessing the database with unique credentials, it makes auditing much easier when questionable data access is discovered: you can track it down to the specific instance of a service based on the SQL username.

Vault makes use of its own internal revocation system to ensure that users become invalid within a reasonable time of the lease expiring.

This page will show a quick start for this secrets engine. For detailed documentation on every path, use vault path-help after mounting the secrets engine.

»Quick Start

The first step to using the mssql secrets engine is to mount it. Unlike the kv secrets engine, the mssql secrets engine is not mounted by default.

$ vault secrets enable mssql
Success! Enabled the mssql secrets engine at: mssql/

Next, we must configure Vault to know how to connect to the MSSQL instance. This is done by providing a DSN (Data Source Name):

$ vault write mssql/config/connection \
    connection_string="server=localhost;port=1433;user id=sa;password=Password!;database=AdventureWorks;app name=vault;"
Success! Data written to: mssql/config/connection

In this case, we've configured Vault with the user "sa" and password "Password!", connecting to an instance at "localhost" on port 1433. It is not necessary that Vault has the sa login, but the user must have privileges to create logins and manage processes. The fixed server roles securityadmin and processadmin are examples of built-in roles that grant these permissions. The user also must have privileges to create database users and grant permissions in the databases that Vault manages. The fixed database roles db_accessadmin and db_securityadmin are examples or built-in roles that grant these permissions.

Optionally, we can configure the lease settings for credentials generated by Vault. This is done by writing to the config/lease key:

$ vault write mssql/config/lease \
    ttl=1h \
Success! Data written to: mssql/config/lease

This restricts each credential to being valid or leased for 1 hour at a time, with a maximum use period of 24 hours. This forces an application to renew their credentials at least hourly, and to recycle them once per day.

The next step is to configure a role. A role is a logical name that maps to a policy used to generate those credentials. For example, lets create a "readonly" role:

$ vault write mssql/roles/readonly \
    sql="CREATE LOGIN [{{name}}] WITH PASSWORD = '{{password}}'; USE AdventureWorks; CREATE USER [{{name}}] FOR LOGIN [{{name}}]; GRANT SELECT ON SCHEMA::dbo TO [{{name}}]"
Success! Data written to: mssql/roles/readonly

By writing to the roles/readonly path we are defining the readonly role. This role will be created by evaluating the given sql statements. By default, the {{name}} and {{password}} fields will be populated by Vault with dynamically generated values. This SQL statement is creating the named login on the server, user on the AdventureWorks database, and then granting it SELECT on the dbo schema. More complex GRANT queries can be used to customize the privileges of the role.

To generate a new set of credentials, we simply read from that role:

$ vault read mssql/creds/readonly
Key               Value
---               -----
lease_id          mssql/creds/readonly/cdf23ac8-6dbd-4bf9-9919-6acaaa86ba6c
lease_duration    3600
password          ee202d0d-e4fd-4410-8d14-2a78c5c8cb76
username          root-a147d529-e7d6-4a16-8930-4c3e72170b19

By reading from the creds/readonly path, Vault has generated a new set of credentials using the readonly role configuration. Here we see the dynamically generated username and password, along with a one hour lease.

Using ACLs, it is possible to restrict using the mssql secrets engine such that trusted operators can manage the role definitions, and both users and applications are restricted in the credentials they are allowed to read.


The MSSQL secrets engine has a full HTTP API. Please see the MSSQL secrets engine API for more details.