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Versioned Key/Value Secret Engine

The Static Secrets guide introduced the basics of working with key-value secret engine. Vault 0.10 introduced K/V Secrets Engine v2 with Secret Versioning. This guide highlights the key-value secret engine v2 features.

Challenge

The KV secret engine v1 does not provide a way to version or roll back secrets. This made it difficult to recover from unintentional data loss or overwrite when more than one user is writing at the same path.

Solution

Run the version 2 of KV secret engine which can retain a configurable number of secret versions. This enables older versions' data to be retrievable in case of unwanted deletion or updates of the data. In addition, its Check-and-Set operations can be used to protect the data from being overwritten unintentionally.

Versioned KV

Prerequisites

To perform the tasks described in this guide, you need to have a Vault environment. Refer to the Getting Started guide to install Vault. Make sure that your Vault server has been initialized and unsealed.

Policy requirements

To perform all tasks demonstrated in this guide, your policy must include the following permissions:

# Write and manage secrets in key-value secret engine
path "secret*" {
  capabilities = [ "create", "read", "update", "delete", "list" ]
}

# To enable secret engines
path "sys/mounts/*" {
  capabilities = [ "create", "read", "update", "delete" ]
}

If you are not familiar with policies, complete the policies guide.

Steps

This guide demonstrates the basic commands for working with KV secret engine v2.

You will perform the following:

  1. Check the KV secret engine version
  2. Write secrets
  3. Retrieve a specific version of secret
  4. Specify the number of versions to keep
  5. Delete versions of secret
  6. Permanently delete data
  7. Configure automatic data deletion
  8. Check-and-Set Operations

Step 1: Check the KV secret engine version

(Persona: devops)

Before beginning, verify that you are using the v2 of the KV secret engine.

CLI command / API call using cURL / Web UI

CLI command

To check the KV secret engine version:

$ vault secrets list -detailed

Output should include

Path          Type         Accessor           ...   Options           Description
----          ----         --------                 -------           -----------
cubbyhole/    cubbyhole    cubbyhole_9d52aeac ...   map[]             per-token private secret storage
identity/     identity     identity_acea5ba9  ...   map[]             identity store
secret/       kv           kv_2226b7d3        ...   map[version:2]    key/value secret storage
...

Under the Options, the version number is indicated. If the version is 1, you can upgrade it to v2 by executing the following command:

$ vault kv enable-versioning secret/

API call using cURL

To check the KV secret engine version:

$ curl --header "X-Vault-Token: <TOKEN>" \
       <VAULT_ADDRESS>/v1/sys/mounts

Where <TOKEN> is your valid token, and <VAULT_ADDRESS> is where your vault server is running.

Example:

$ curl --header "X-Vault-Token: ..." \
       http://127.0.0.1:8200/v1/sys/mounts | jq
...
  "secret/": {
    "accessor": "kv_f05b8b9c",
    "config": {
      "default_lease_ttl": 0,
      "force_no_cache": false,
      "max_lease_ttl": 0,
      "plugin_name": ""
    },
    "description": "key/value secret storage",
    "local": false,
    "options": {
      "version": "2"
    },
    "seal_wrap": false,
    "type": "kv"
  },
...

The indicated version should be 2. If the version is 1, upgrade it to v2.

$ cat payload.json
{
  "options": {
      "version": "2"
  }
}

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data @payload.json \
       http://127.0.0.1:8200/v1/sys/mounts/secret/tune

Web UI

Open a web browser and launch the Vault UI (e.g. http://127.0.0.1:8200/ui) and then login.

Web UI

If secret/ does not indicates v2, you can upgrade it from v1 to v2. Click the Vault CLI shell icon (>_) to open a command shell. Execute the following command to upgrade it to v2: vault write sys/mounts/secret/tune version=2

Tune KV Versions

Click the icon (>_) again to hide the shell.

Alternatively, you can enable KV secret engine v2 at another path by clicking Enable new engine. Select KV from the list, and then click Next.

Enabling kv-v2

Under the Version, be sure to select 2.

Enabling kv-v2

Click Enable Engine to complete.

Step 2: Write Secrets

To understand how the versioning works, let's write some test data.

CLI command / API call using cURL / Web UI

CLI command

To operate with key/value secrets engine, run vault kv commands. Execute the following command to write some secrets:

$ vault kv put secret/customer/acme name="ACME Inc." contact_email="jsmith@acme.com"
Key              Value
---              -----
created_time     2018-04-14T00:05:47.115378933Z
deletion_time    n/a
destroyed        false
version          1

To update the existing secret, run the vault kv put command again:

$ vault kv put secret/customer/acme name="ACME Inc." contact_email="john.smith@acme.com"
Key              Value
---              -----
created_time     2018-04-14T00:13:35.296018431Z
deletion_time    n/a
destroyed        false
version          2

Now you have two versions of the secret/customer/acme data. Run vault kv get to read the data.

$ vault kv get secret/customer/acme
====== Metadata ======
Key              Value
---              -----
created_time     2018-04-14T00:13:35.296018431Z
deletion_time    n/a
destroyed        false
version          2

======== Data ========
Key              Value
---              -----
contact_email    john.smith@acme.com
name             ACME Inc.

Writing to a key will replace the existing value, and sub-fields are not merged together. Therefore, running the following command can result in an unintentional data loss:

vault kv put secret/customer/acme contact_email="admin@acme.com"

To update the contact_email address without changing the name, execute the vault kv patch command instead:

$ vault kv patch secret/customer/acme contact_email="admin@acme.com"

API call using cURL

Write some data at secret/customer/acme:

$ tee payload.json <<EOF
{
  "data": {
    "name": "ACME Inc.",
    "contact_email": "jsmith@acme.com"
  }
}
EOF

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data @payload.json \
       http://127.0.0.1:8200/v1/secret/data/customer/acme

Notice that the endpoint for KV v2 is /secret/data/<path>; therefore to write secrets at secret/customer/acme, the API endpoint becomes /secret/data/customer/acme.

Update the secret to create another version:

$ tee payload.json <<EOF
{
  "data": {
    "name": "ACME Inc.",
    "contact_email": "john.smith@acme.com"
  }
}
EOF

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data @payload.json \
       http://127.0.0.1:8200/v1/secret/data/customer/acme

Now you have two versions of the secret/customer/acme data. Read back the secret.

$ curl --header "X-Vault-Token: ..." \
       http://127.0.0.1:8200/v1/secret/data/customer/acme
{
   "request_id": "7233b69d-35d9-6c1b-ae81-9a679a03082d",
   "lease_id": "",
   "renewable": false,
   "lease_duration": 0,
   "data": {
     "data": {
       "contact_email": "john.smith@acme.com",
       "name": "ACME Inc."
     },
     "metadata": {
       "created_time": "2018-04-14T00:59:11.27903511Z",
       "deletion_time": "",
       "destroyed": false,
       "version": 2
     }
   },
   "wrap_info": null,
   "warnings": null,
   "auth": null
}

Web UI

In the Web UI, select secret/ and then click Create secret. Enter the secrets. You can click on the sensitive information toggle to show or hide the entered secret values.

Write Secret

NOTE: Notice that the Maximum Number of Versions is set to 10 by default.

Click Save.

To update the existing secret, select Create new version, change the contact_email value, and then click Save.

Write Secret

Step 3: Retrieve a Specific Version of Secret

You may run into a situation where you need to view the secret before an update.

CLI command / API call using cURL / Web UI

CLI command

To retrieve the version 1 of the secret written at secret/customer/acme:

$ vault kv get -version=1 secret/customer/acme
====== Metadata ======
Key              Value
---              -----
created_time     2018-04-14T00:05:47.115378933Z
deletion_time    n/a
destroyed        false
version          1

======== Data ========
Key              Value
---              -----
contact_email    jsmith@acme.com
name             ACME Inc.

To read the metadata of secret/customer/acme:

$ vault kv metadata get secret/customer/acme
========== Metadata ==========
Key                     Value
---                     -----
cas_required            false
created_time            2019-07-31T05:57:32.959408Z
current_version         2
delete_version_after    0s
max_versions            0
oldest_version          0
updated_time            2019-07-31T05:58:45.338017Z

====== Version 1 ======
Key              Value
---              -----
created_time     2019-07-31T05:57:32.959408Z
deletion_time    n/a
destroyed        false

====== Version 2 ======
Key              Value
---              -----
created_time     2019-07-31T05:58:06.354642Z
deletion_time    n/a
destroyed        false

API call using cURL

To retrieve the version 1 of the secret written at secret/customer/acme:

$ curl --header "X-Vault-Token: ..." \
       http://127.0.0.1:8200/v1/secret/data/customer/acme?version=1 | jq
{
 "request_id": "3bf5a2c1-d89b-9dd5-9bb5-0bc61a4a6d83",
 "lease_id": "",
 "renewable": false,
 "lease_duration": 0,
 "data": {
   "data": {
     "contact_email": "jsmith@acme.com",
     "name": "ACME Inc."
   },
   "metadata": {
     "created_time": "2018-04-14T00:05:47.115378933Z",
     "deletion_time": "",
     "destroyed": false,
     "version": 1
   }
 },
 "wrap_info": null,
 "warnings": null,
 "auth": null
}

To read the metadata of secret/customer/acme:

$ curl --header "X-Vault-Token: ..." \
       http://127.0.0.1:8200/v1/secret/metadata/customer/acme | jq
{
 "request_id": "34708262-59cd-9a94-247f-3b1db0909050",
 "lease_id": "",
 "renewable": false,
 "lease_duration": 0,
 "data": {
    "cas_required": false,
    "created_time": "2019-07-31T05:57:32.959408Z",
    "current_version": 2,
    "delete_version_after": "0s",
    "max_versions": 0,
    "oldest_version": 0,
    "updated_time": "2019-07-31T05:58:45.338017Z",
    "versions": {
      "1": {
        "created_time": "2019-07-31T05:57:32.959408Z",
        "deletion_time": "",
        "destroyed": false
      },
      "2": {
        "created_time": "2019-07-31T05:58:06.354642Z",
        "deletion_time": "",
        "destroyed": false
      }
   }
 },
 "wrap_info": null,
 "warnings": null,
 "auth": null
}

Web UI

Select History and then Version 1

Read Version 1

The version changes from Version 2 to Version 1. To view the raw values, click on the sensitive information toggle.

Read Version 1

You can create a new version of the secrets based on an older version. Select History > View version history. Select the version you wish to based the data on, and then select Create new version from 1.

Create New Version

This can help revert an older version of the secrets.

Step 4: Specify the number of versions to keep

By default, the kv-v2 secret engine keeps up to 10 versions. Let's limit the maximum number of versions to keep to be 4.

CLI command / API call using cURL / Web UI

CLI command

To set the secret/ to keep up to 4 versions:

$ vault write secret/config max_versions=4
Success! Data written to: secret/config

# View the configuration settings
$ vault read secret/config
Key             Value
---             -----
cas_required    false
max_versions    4

Or, to limit the number of versions only on the secret/customer/acme path rather than the entire secret/ engine:

$ vault kv metadata put -max-versions=4 secret/customer/acme

Overwrite the data a few more times to see what happens to its metadata.

$ vault kv metadata get secret/customer/acme
======= Metadata =======
Key                Value
---                -----
created_time       2018-04-14T00:42:25.677078177Z
current_version    6
max_versions       0
oldest_version     3
updated_time       2018-04-16T00:17:23.930473344Z

====== Version 3 ======
Key              Value
---              -----
created_time     2018-04-16T00:15:59.880368849Z
deletion_time    n/a
destroyed        false

====== Version 4 ======
Key              Value
---              -----
created_time     2018-04-16T00:16:18.941331243Z
deletion_time    n/a
destroyed        false

====== Version 5 ======
Key              Value
---              -----
created_time     2018-04-16T00:16:34.407951572Z
deletion_time    n/a
destroyed        false

====== Version 6 ======
Key              Value
---              -----
created_time     2018-04-16T00:17:23.930473344Z
deletion_time    n/a
destroyed        false

In this example, the current version is 6. Notice that version 1 and 2 do not show up in the metadata. Because the kv secret engine is configured to keep only 4 versions, the oldest two versions are permanently deleted and you won't be able to read them.

$ vault kv get -version=1 secret/customer/acme
No value found at secret/data/customer/data

API call using cURL

To set the secret/ to keep up to 4 versions:

$ tee payload.json<<EOF
{
  "max_versions": 4,
  "cas_required": false
}
EOF

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data @payload.json
       http://127.0.0.1:8200/v1/secret/config

To view the configuration:

$ curl --header "X-Vault-Token: ..." \
       http://127.0.0.1:8200/v1/secret/config | jq
{
 "request_id": "8addfed1-41eb-6a19-8342-93f493c51538",
 "lease_id": "",
 "renewable": false,
 "lease_duration": 0,
 "data": {
   "cas_required": false,
   "max_versions": 4
 },
 "wrap_info": null,
 "warnings": null,
 "auth": null
}

To limit the number of versions only on the secret/customer/acme path rather than the entire secret/ engine:

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data @payload.json
       http://127.0.0.1:8200/v1/secret/metadata/customer/acme

Invoke the secret/metadata/customer/acme endpoint instead.

Overwrite the data a few more times to see what happens to the data.

$ curl --header "X-Vault-Token: ..." \
       http://127.0.0.1:8200/v1/secret/metadata/customer/acme | jq
{
 ...
 "data": {
   "created_time": "2018-04-14T00:42:25.677078177Z",
   "current_version": 6,
   "max_versions": 0,
   "oldest_version": 3,
   "updated_time": "2018-04-16T00:17:23.930473344Z",
   "versions": {
     "3": {
       "created_time": "2018-04-16T00:15:59.880368849Z",
       "deletion_time": "",
       "destroyed": false
     },
     "4": {
       "created_time": "2018-04-16T00:16:18.941331243Z",
       "deletion_time": "",
       "destroyed": false
     },
     "5": {
       "created_time": "2018-04-16T00:16:34.407951572Z",
       "deletion_time": "",
       "destroyed": false
     },
     "6": {
       "created_time": "2018-04-16T00:17:23.930473344Z",
       "deletion_time": "",
       "destroyed": false
     }
   }
 },
 ...
}

In this example, the current version is 6. Notice that version 1 and 2 do not show up in the metadata. Because the kv secret engine is configured to keep only 4 versions, the oldest two versions are permanently deleted and you won't be able to read them.

$ curl --header "X-Vault-Token: ..." \
       http://127.0.0.1:8200/v1/secret/data/customer/acme?version=1 | jq
{
 "errors": []
}

Web UI

Click the Vault CLI shell icon (>_) to open a command shell. Execute the following command to tune the maximum number of versions to keep: vault write secret/config max_versions=4

Tune Max Versions

Click the icon (>_) again to hide the shell.

Overwrite the data a few more times to see what happens to its versions.

Tune Max Versions

In this example, the current version is 6. Notice that version 1 and 2 do not show up in the metadata. Because the kv secret engine is configured to keep only 4 versions, the oldest two versions are permanently deleted and you won't be able to read them.

Step 5: Delete versions of secret

CLI command / API call using cURL / Web UI

CLI command

Let's delete versions 4 and 5:

$ vault kv delete -versions="4,5" secret/customer/acme
Success! Data deleted (if it existed) at: secret/customer/acme

# Check the metadata
$ vault kv metadata get secret/customer/acme
...
====== Version 4 ======
Key              Value
---              -----
created_time     2018-04-16T00:12:25.404198622Z
deletion_time    2018-04-16T01:04:01.160426888Z
destroyed        false

====== Version 5 ======
Key              Value
---              -----
created_time     2018-04-16T00:12:47.527981267Z
deletion_time    2018-04-16T01:04:01.160427742Z
destroyed        false
...

The metadata on versions 4 and 5 reports its deletion timestamp (deletion_time); however, the destroyed parameter is set to false.

If version 5 was deleted by mistake and you wish to recover, invoke the vault kv undelete command:

$ vault kv undelete -versions=5 secret/customer/acme
Success! Data written to: secret/undelete/customer/acme

API call using cURL

Let's delete versions 4 and 5:

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data '{ "versions":[4,5] }'
       http://127.0.0.1:8200/v1/secret/delete/customer/acme

# Check the metadata
$ curl --header "X-Vault-Token: ..." \
      http://127.0.0.1:8200/v1/secret/metadata/customer/acme | jq
...
"4": {
   "created_time": "2018-04-16T00:16:18.941331243Z",
   "deletion_time": "2018-04-16T01:17:42.003111567Z",
   "destroyed": false
 },
 "5": {
   "created_time": "2018-04-16T00:16:34.407951572Z",
   "deletion_time": "2018-04-16T01:17:42.003111978Z",
   "destroyed": false
 },
...

The metadata on versions 4 and 5 reports its deletion timestamp (deletion_time); however, the destroyed parameter is set to false.

If version 5 was deleted by mistake and you wish to recover, invoke the /secret/undelete endpoint:

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data '{ "versions":[5] }'
       http://127.0.0.1:8200/v1/secret/undelete/customer/acme

Web UI

Let's delete versions 4 and 5.

At the secret/customer/acme path, select History > View version history. Expand the menu for Version 5 and select Delete version.

Delete Versions

At the confirmation dialog, click Delete to proceed. Repeat the steps for Version 4. Now, Version 4 and 5 should be marked as deleted.

If version 5 was deleted by mistake and you wish to recover, select Undelete version from its menu.

Step 6: Permanently delete data

CLI command / API call using cURL / Web UI

CLI command

To permanently delete a version of secret:

$ vault kv destroy -versions=4 secret/customer/acme
Success! Data written to: secret/destroy/customer/acme

# Check the metadata
$ vault kv metadata get secret/customer/acme
...
====== Version 4 ======
Key              Value
---              -----
created_time     2018-04-16T00:12:25.404198622Z
deletion_time    2018-04-16T01:04:01.160426888Z
destroyed        true
...

The metadata indicates that Version 4 is destroyed.

If you wish to destroy all the keys and versions at secret/customer/acme, invoke the vault kv metadata delete command:

$ vault kv metadata delete secret/customer/acme
Success! Data deleted (if it existed) at: secret/metadata/customer/acme

API call using cURL

To permanently delete a version of secret:

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data '{ "versions":[4] }'
       http://127.0.0.1:8200/v1/secret/destroy/customer/acme

# Check the metadata
$ curl --header "X-Vault-Token: ..." \
      http://127.0.0.1:8200/v1/secret/metadata/customer/acme | jq
...
  "4": {
    "created_time": "2018-04-16T00:16:18.941331243Z",
    "deletion_time": "2018-04-16T01:17:42.003111567Z",
    "destroyed": true
  },
...

The metadata indicates that Version 4 is destroyed.

If you wish to destroy all the keys and versions at secret/customer/acme, invoke the secret/metadata endpoint:

$ curl --header "X-Vault-Token: ..." \
       --request DELETE
       http://127.0.0.1:8200/v1/secret/metadata/customer/acme

Web UI

To permanently delete a version of secret, simply select Permanently destroy version from its menu.

Destroy Versions

Step 7: Configure automatic data deletion

As of Vault 1.2, you can configure the length of time before a version gets deleted. For example, if your organization requires data to be deleted after 10 days from its creation, you can configure the K/V v2 secrets engine to do so by setting the delete_version_after parameter.

CLI command / API call using cURL

CLI command

For the purpose of demonstration, keep the delete_version_after to 40 seconds.

$ vault kv metadata put -delete-version-after=40s secret/test
Success! Data written to: secret/metadata/test

To test, write some test data:

$ vault kv put secret/test message="data1"

$ vault kv put secret/test message="data2"

$ vault kv put secret/test message="data3"

NOTE: You can use upper-arrow key to recover the previously executed command.

Now, check the metadata:

$ vault kv metadata get secret/test

========== Metadata ==========
Key                     Value
---                     -----
cas_required            false
created_time            2019-07-31T06:51:49.726188Z
current_version         3
delete_version_after    40s
max_versions            0
oldest_version          0
updated_time            2019-07-31T06:55:54.203923Z

====== Version 1 ======
Key              Value
---              -----
created_time     2019-07-31T06:55:37.795176Z
deletion_time    2019-07-31T06:56:17.795176Z
destroyed        false

====== Version 2 ======
Key              Value
---              -----
created_time     2019-07-31T06:55:41.207457Z
deletion_time    2019-07-31T06:56:21.207457Z
destroyed        false

====== Version 3 ======
Key              Value
---              -----
created_time     2019-07-31T06:55:43.811997Z
deletion_time    2019-07-31T06:56:23.811997Z
destroyed        false

Notice that the deletion_time is set on each version. After 40 seconds, the data gets deleted automatically. (NOTE: The data gets deleted, but not destroyed.)

$ vault kv get -version=1 secret/test
====== Metadata ======
Key              Value
---              -----
created_time     2019-07-31T06:55:37.795176Z
deletion_time    2019-07-31T06:56:17.795176Z
destroyed        false
version          1

API call using cURL

For the purpose of demonstration, keep the delete_version_after to 40 seconds.

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data '{ "delete_version_after": "40s" }'
       http://127.0.0.1:8200/v1/secret/metadata/test

To test, write some test data:

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data '{"data": {"message": "data1"}}' \
       http://127.0.0.1:8200/v1/secret/data/test

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data '{"data": {"message": "data2"}}' \
       http://127.0.0.1:8200/v1/secret/data/test

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data '{"data": {"message": "data3"}}' \
       http://127.0.0.1:8200/v1/secret/data/test

Now, check the metadata:

$ curl --header "X-Vault-Token: ..." \
       http://127.0.0.1:8200/v1/secret/metadata/test | jq
{
  ...
  "data": {
    "cas_required": false,
    "created_time": "2019-07-31T07:10:17.162211Z",
    "current_version": 3,
    "delete_version_after": "40s",
    "max_versions": 0,
    "oldest_version": 0,
    "updated_time": "2019-07-31T07:11:32.750329Z",
    "versions": {
      "1": {
        "created_time": "2019-07-31T07:10:57.59863Z",
        "deletion_time": "2019-07-31T07:11:37.59863Z",
        "destroyed": false
      },
      "2": {
        "created_time": "2019-07-31T07:11:25.145534Z",
        "deletion_time": "2019-07-31T07:12:05.145534Z",
        "destroyed": false
      },
      "3": {
        "created_time": "2019-07-31T07:11:32.750329Z",
        "deletion_time": "2019-07-31T07:12:12.750329Z",
        "destroyed": false
      }
    }
  },
  ...
}

Notice that the deletion_time is set on each version. After 40 seconds, the data gets deleted automatically. (NOTE: The data gets deleted, but not destroyed.)

$ curl --header "X-Vault-Token: ..." \
       http://127.0.0.1:8200/v1/secret/data/test?version=1 | jq
{
  ...
  "data": {
    "data": null,
    "metadata": {
      "created_time": "2019-07-31T07:10:57.59863Z",
      "deletion_time": "2019-07-31T07:11:37.59863Z",
      "destroyed": false,
      "version": 1
    }
  },
  ...
}

Step 8: Check-and-Set Operations

The v2 of KV secret engine supports a Check-And-Set operation to prevent unintentional secret overwrite. When you pass the cas flag to Vault, it first checks if the key already exists.

By default, Check-And-Set operation is not enabled on the KV secret engine; therefore write is always allowed (no checking is performed).

$ vault read secret/config

Key             Value
---             -----
cas_required    false
max_versions    0

CLI command / API call using cURL / Web UI

CLI command

To enable the Check-And-Set operation:

# Enable cas_requied on the secret engine mounted at secret/
$ vault write secret/config cas-required=true

# Enable cas_requied only on the secret/partner path
$ vault kv metadata put -cas-required=true secret/partner

Once check-and-set is enabled, every write operation requires cas value to be passed. If you are sure that you want to overwrite the existing key-value, set cas to match the current version. Set cas to 0 if you want to write the secret only if the key does not exists.

Example:

# To write if the key does not already exists
$ vault kv put -cas=0 secret/partner name="Example Co." partner_id="123456789"
Key              Value
---              -----
created_time     2018-04-16T22:58:15.798753323Z
deletion_time    n/a
destroyed        false
version          1

# To overwrite the secret, you must specify the current version with -cas flag
$ vault kv put -cas=1 secret/partner name="Example Co." partner_id="ABCDEFGHIJKLMN"
Key              Value
---              -----
created_time     2018-04-16T23:00:28.66552289Z
deletion_time    n/a
destroyed        false
version          2

API call using cURL

To enable the Check-And-Set operation:

$ tee payload.json<<EOF
{
  "max_versions": 10,
  "cas_required": true
}
EOF

# Enable cas_requied on the secret engine mounted at secret/
$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data @payload.json
       http://127.0.0.1:8200/v1/secret/config

# Enable cas_requied only on the secret/partner path
$ curl --header "X-Vault-Token: ..." \
      --request POST \
      --data @payload.json
      http://127.0.0.1:8200/v1/secret/metadata/partner

Once check-and-set is enabled, every write operation requires cas value to be passed. If you are sure that you want to overwrite the existing key-value, set cas to match the current version. Set cas to 0 if you want to write the secret only if the key does not exists.

Example:

# Write if the key does not already exists
$ tee payload.json <<EOF
{
  "options": {
    "cas": 0
  },
  "data": {
    "name": "Example Co.",
    "partner_id": "123456789"
  }
}
EOF

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data @payload.json \
       http://127.0.0.1:8200/v1/secret/data/partner

# To overwrite the secret, you must pass the current version
$ tee payload.json <<EOF
{
  "options": {
    "cas": 1
  },
  "data": {
    "name": "Example Co.",
    "partner_id": "ABCDEFGHIJKLMN"
  }
}
EOF

$ curl --header "X-Vault-Token: ..." \
       --request POST \
       --data @payload.json \
       http://127.0.0.1:8200/v1/secret/data/partner

Web UI

To enable the Check-And-Set operation, select the Require Check and Set check-box when you create secrets.

Destroy Versions

NOTE: UI will always write a new version with cas even if the check-and-set operation is not required.

Help and Reference