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159 lines
6.5 KiB
Plaintext
159 lines
6.5 KiB
Plaintext
---
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layout: docs
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page_title: Username Templating
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description: >-
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Username templating are used in some secret engines to allow operators to define
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how dynamic usernames are generated.
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---
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# Username Templating
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Some of the secrets engines that generate dynamic users for external systems provide the ability for Vault operators
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to customize how usernames are generated for said external systems. This customization feature uses the
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[Go template language](https://golang.org/pkg/text/template/). This page describes the basics of using these templates
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for username generation but does not go into great depth of using the templating language for more advanced usages.
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See the API documentation for the given secret engine to determine if it supports username templating and for more
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details on using it with that engine.
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~> When customizing how usernames are generated, take care to ensure you have enough randomness to ensure uniqueness
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otherwise multiple calls to create the credentials may interfere with each other.
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In addition to the functionality built into the Go template language, a number of additional functions are available:
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## Available Functions
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### String/Character Manipulation
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`lowercase` - Lowercases the input value.<br/>
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**Example**: `{{.FieldName | lowercase}}`
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`replace` - Find/replace on the input value.<br/>
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**Example**: `{{.FieldName | replace - _}}`
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`truncate` - truncates the input value to the specified number of characters.<br/>
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**Example**: `{{.FieldName | truncate 10}}`
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`truncate_sha256` - Truncates the input value to the specified number of characters. The last 8 characters of the
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new value will be replace by the first 8 characters of the SHA256 hash of the truncated characters.<br/>
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**Example**: `{{.FieldName | truncate_sha256 20}}`. If `FieldName` is `abcdefghijklmnopqrstuvwxyz`, all characters after
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the 12th (`l`) are removed and SHA256 hashed (`872808ffbf...1886ca6f20`).
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The first 8 characters of the hash (`872808ff`) are then appended to the end of the first 12 characters from the
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original value: `abcdefghijkl872808ff`.
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`uppercase` - Uppercases the input value.<br/>
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**Example**: `{{.FieldName | uppercase}}`
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### Generating Values
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`random` - Generates a random string from lowercase letters, uppercase letters, and numbers. Must include a
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number indicating how many characters to generate.<br/>
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**Example**: `{{random 20}}` generates 20 random characters
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`timestamp` - The current time. Must provide a formatting string based on Go’s [time package](https://golang.org/pkg/time/).<br/>
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**Example**: `{{timestamp "2006-01-02T15:04:05Z"}}`
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`unix_time` - The current unix timestamp (number of seconds since Jan 1 1970).<br/>
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**Example**: `{{unix_time}}`
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`unix_time_millis` - The current unix timestamp in milliseconds.<br/>
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**Example**: `{{unix_time_millis}}`
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`uuid` - Generates a random UUID.<br/>
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**Example**: `{{uuid}}`
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### Hashing
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`base64` - Base64 encodes the input value.<br/>
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**Example**: `{{.FieldName | base64}}`
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`sha256` - SHA256 hashes the input value.<br/>
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**Example**: `{{.FieldName | sha256}}`
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## Examples
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Each secret engine provides a different set of data to the template. Please see the associated secret engine's
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documentation for details on what values are provided to the template. The examples below are modeled after the
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[Database engine's](/docs/secrets/databases) data, however the specific fields that are provided from a given engine
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may differ from these examples. Additionally, the time is assumed to be 2009-02-13 11:31:30PM GMT
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(unix timestamp: 1234567890) and random characters are the ordered english alphabet: `abcdefghijklmnopqrstuvwxyz`.
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-> Note: The space between `{{`/`}}` and the values/functions are optional.
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For instance: `{{.DisplayName}}` is equivalent to `{{ .DisplayName }}`
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| Field name | Value |
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| ------------- | ------------------------- |
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| `DisplayName` | `token-with-display-name` |
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| `RoleName` | `my_custom_database_role` |
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To reference either of these fields, a `.` must be put in front of the field name: `{{.DisplayName}}`. Custom functions
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do not include a `.` in front of them: `{{random 20}}`.
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### Basic Example
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**Template**:
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```
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{{.DisplayName}}_{{.RoleName}}
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```
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**Username**:
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```
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token-with-display-name_my_custom_database_role
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```
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This is a basic example that references the two fields that are provided to the template. In simplest terms, this is
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a simple string substitution.
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~> This example does not have any randomness and should not be used when generating dynamic usernames. The purpose is to
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demonstrate referencing data within the Go template language.
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### Custom Functions
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**Template**:
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```
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FOO_{{.DisplayName | replace "-" "_" | uppercase}}_{{.RoleName | replace "-" "_" | uppercase}}_{{timestamp "2006_01_02T15_04_05Z" | replace "-" "_"}}
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```
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**Username**:
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```
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FOO_TOKEN_WITH_DISPLAY_NAME_MY_CUSTOM_DATABASE_ROLE_2009_02_13T11_31_30Z_0700
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```
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`{{.DisplayName | replace "-" "_" | uppercase}}` - Replaces all dashes with underscores and then uppercases the display name.<br/>
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`{{.RoleName | replace "-" "_" | uppercase}}` - Replaces all dashes with underscores and then uppercases the role name.<br/>
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`{{timestamp "2006_01_02T15_04_05Z" | replace "-" "_"}}` - Generates the current timestamp using the provided format and
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replaces all dashes with underscores.
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### Truncating to Maximum Length
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**Template**:
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```
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{{printf "v_%s_%s_%s_%s" (.DisplayName | truncate 8) (.RoleName | truncate 8) (random 20) (unix_time) | truncate 45}}
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```
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**Username**:
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```
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v_token-wi_my_custo_abcdefghijklmnopqrst_1234
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```
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`.DisplayName | truncate 8` truncates the display name to 8 characters (`token-wi`).<br/>
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`.RoleName | truncate 8` truncates the role name to 8 characters (`my_custo`).<br/>
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`random 20` generates 20 random characters `abcdefghijklmnopqrst`.<br/>
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`unix_time` generates the current timestamp as the number of seconds since January 1, 1970 (`1234567890`).<br/>
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Each of these values are passed to `printf "v_%s_%s_%s_%s"` which prepends them with `v_` and puts an underscore between
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each field. This results in `v_token-wi_my_custo_abcdefghijklmnopqrst_1234567890`. This value is then passed to
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`truncate 45` where the last 6 characters are removed which results in `v_token-wi_my_custo_abcdefghijklmnopqrst_1234`.
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## Learn
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Refer to the following tutorials for step-by-step instructions.
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- [Database Secrets Engine with MongoDB](https://learn.hashicorp.com/tutorials/vault/database-mongodb#customize-the-generated-username-schema)
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- [Dynamic Secrets: Database Secrets Engine](https://learn.hashicorp.com/tutorials/vault/database-secrets#define-a-username-template)
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