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Out-of-band communication via E-Mail and SMS

Ory Kratos sends out-of-band messages via SMS or E-Mail. The following exemplary use cases require these messages:

  • Send an account activation email
  • Verify an E-Mail address or mobile phone number using SMS
  • Preventing Account Enumeration Attacks
  • Sending a 2FA Codes

Mail courier​

Ory Kratos processes email dispatch using a mail courier worker, which must run as a singleton in order to process the mail queue. It can be run as a background worker on a single-instance Kratos setup or as a distinct singleton foreground worker in multi-instance deployments.

Single instance​

To run the mail courier in the background on your single Kratos instance, add the --watch-courier flag to your kratos serve command, as outlined in the CLI docs

Multi-instance​

If you're running multiple instances of Kratos (for example replicated Kubernetes deployment), you need to run the mail courier as a separate singleton job. The courier can be started with the kratos courier watch command (CLI docs).

Sending E-Mails via SMTP​

To have E-Mail delivery running with Ory Kratos requires an SMTP server. This is set up in the configuration file using an absolute URL with the smtp or smtps scheme:

path/to/my/kratos/config.yml
# kratos -c path/to/my/kratos/config.yml serve
courier:
  smtp:
    connection_uri: smtps://foo:bar@my-smtp-server:1234/
    # Examples:
    # - "smtp://foo:bar@my-mailserver:1234/?disable_starttls=true
    #   (NOT RECOMMENDED: Cleartext smtp for devel and legacy infrastructure
    #   only)"
    # - smtp://foo:bar@my-mailserver:1234/ (Explicit StartTLS with certificate
    #   trust verification)
    # - "smtp://foo:bar@my-mailserver:1234/?skip_ssl_verify=true (NOT
    #   RECOMMENDED: Explicit StartTLS without certificate trust verification)"
    # - smtps://foo:bar@my-mailserver:1234/ (Implicit TLS with certificate trust
    #   verification)
    # - "smtps://foo:bar@my-mailserver:1234/?skip_ssl_verify=true (NOT
    #   RECOMMENDED: Implicit TLS without certificate trust verification)"
    # - "smtps://subdomain.my-mailserver:1234/?server_name=my-mailserver (allows TLS to
    #   work if the server is hosted on a sudomain and uses a non-wildcard domain certificate)"

Sender Address and Template Customization​

You can customize the sender address and email templates by overriding path to the templates folder. See more about custom templates in templates section.

path/to/my/kratos/config.yml
# kratos -c path/to/my/kratos/config.yml serve
courier:
  ## SMTP Sender Address ##
  #
  # The recipient of an email will see this as the sender address.
  #
  # Default value: no-reply@ory.kratos.sh
  #
  # Set this value using environment variables on
  # - Linux/macOS:
  #    export COURIER_SMTP_FROM_ADDRESS=<value>
  # - Windows Command Line (CMD):
  #    > set COURIER_SMTP_FROM_ADDRESS=<value>
  #
  smtp:
    from_address: no-reply@ory.kratos.sh
  ## Override message templates ##
  #
  # You can override certain or all message templates by pointing this key to the path where the templates are located.
  #
  # Examples:
  # - /conf/courier-templates
  #
  # Set this value using environment variables on
  # - Linux/macOS:
  #    export COURIER_TEMPLATE_OVERRIDE_PATH=<value>
  # - Windows Command Line (CMD):
  #    > set COURIER_TEMPLATE_OVERRIDE_PATH=<value>
  #
  template_override_path: /conf/courier-templates

  ## Override with remote templates ##
  #
  # You can specify specific template values to override or the whole template
  #
  # Supported templates are:
  # - verification
  #   - valid
  #   - invalid
  # - recovery
  #   - valid
  #   - invalid
  #
  # Each template supports the following layout. A singular key can be specified under `email` to override the defaults.
  # When specifying `body`, however, Kratos expects `html` and `plaintext` to be set.
  # email:
  #   subject: http(s)://, file://, base64://
  #   body:
  #     html: http(s)://, file://, base64://
  #     plaintext: http(s)://, file://, base64://
  templates:
    # we can specify here
    verification:
      valid:
        email:
          body:
            # plaintext and html are required when overriding the body
            html: https://some-remote-resource/gotmpl
            plaintext: base64://SGV5IHlvdSBkZWNvZGVkIG1lIDop
          # optional
          subject: file://some-file/subject.gotmpl
      # we can also omit the `invalid` field here if you wish to use the default built-in templates
      # or template_override_path
      invalid:
        # same configuration structure as valid
    # this is also optional and can be omitted in preference for the default built-in templates
    # or template_override_path
    recovery:
      # the configuration structure is the same as the verification

Custom SMTP Headers​

You can configure custom SMTP headers. For example, if integrating with AWS SES SMTP interface, the headers can be configured for cross-account sending:

path/to/my/kratos/config.yml
# kratos -c path/to/my/kratos/config.yml serve
courier:
  smtp:
    headers:
      X-SES-SOURCE-ARN: arn:aws:ses:us-west-2:123456789012:identity/example.com
      X-SES-FROM-ARN: arn:aws:ses:us-west-2:123456789012:identity/example.com
      X-SES-RETURN-PATH-ARN: arn:aws:ses:us-west-2:123456789012:identity/example.com

Certificate based authentication​

If your SMTP server enforces certificate based authentication, you can configure the client certificate and client private key to use to connect to the server. The files must contain PEM encoded data:

path/to/my/kratos/config.yml
# kratos -c path/to/my/kratos/config.yml serve
courier:
  smtp:
    client_cert_path: /somepath/client.cert
    client_key_path: /somepath/client.key

Custom SMTP HELO/EHLO identifier​

If your SMTP server requires a unique identifier for the HELO/EHLO command, you can configure the identifier. Some SMTP relays (e.g. Gmail / Google Workspace) may close the connection for generic identifiers like localhost. The identifier should usually be the domain name of the sending host. If the identifier is not configured, localhost is used per default.

path/to/my/kratos/config.yml
courier:
  smtp:
    local_name: exmaple.org

Sending SMS​

For sending SMS Ory Kratos uses an external SMS gateway, which must have HTTP API (such as Twilio, your local SMS sender, or your own microservice). Request method, headers, body, and content-type are fully configurable using options below.

Configuration​

Default configuration of Ory Kratos doesn't include sending SMS. To enable it you need to set "enabled" flag to true, sender URL, authorization (if needed) and request body format.

Sender phone number​

SMS message will come to the recipient from this phone number. Depending on your SMS sender settings you can use letters here (for example "Your Org Name"). Default value is equal to "Ory Kratos".

path/to/my/kratos/config.yml
# kratos -c path/to/my/kratos/config.yml serve
courier:
  sms:
    from: "+12065550110"

Request configuration​

path/to/my/kratos/config.yml
# kratos -c path/to/my/kratos/config.yml serve
courier:
  sms:
    request_config:
      url: https://api.twilio.com/2010-04-01/Accounts/YourAccountID/Messages.json
      method: POST
      body: file://./path/to/path/to/my/kratos/config/twilio.request.jsonnet
      header:
        "Content-Type": "application/x-www-form-urlencoded"
      auth:
        type: basic_auth
        config:
          user: YourUsername
          password: YourPass

The configuration consists of:

  • url - the URL, which should be called (mandatory). It needs to be absolute, start with http:// or https:// scheme, and include path part - for example "https://api.sender.com/v1/message".
  • method - the HTTP method (GET, POST, ...) (mandatory)
  • body - URI of a JsonNet template, used to render the payload to send (optional). Use a file://path/to/body.jsonnet URL for referring to local files. This property is ignored for HTTP methods, which don't support sending of HTTP body payloads (TRACE).
  • auth - configuration of authentication and authorization mechanisms to be used by request

Courier binds the from, to, and body variables into the JsonNet template. These variables are available through a ctx object. For example to create a body looking like { to: "<some-number>" } to be sent to the SMS provider endpoint, the jsonnet template would look like this:

function(ctx) {
  from: ctx.from,
  to: ctx.to,
  body: ctx.body
}

Authentication and Authorization​

For auth following mechanisms are supported:

  • Authentication via an Api Key. Type must be set to api_key.
  • Authentication via Basic Authentication. Type must be set to basic_auth.

For api_key the config looks as follows:

name: Some-Name
value: The-Value-of-My-Key
in: header # alternatively cookie

All properties are mandatory.

For basic_auth the config looks as follows:

user: My-User
password: My-Pass-Value

All properties are mandatory.

Message templates​

Ory Kratos comes with built-in templates. If you wish to define your own, custom templates, you can use two methods.

  1. Define each template individually through templates as shown above for recovery.invalid, recovery.valid, verification.invalid and verification.valid. None of the configurations listed are mandatory and will always fallback to the build-in templates or what's defined by template_override_path.
  2. Define template_override_path, as shown above, to indicate where your custom templates are located. This will become the <template-root> for your custom templates, as indicated below.

Remote Templates​

Templates can be added through http://, file:// and base64:// URIs in the configurations. The only mandatory fields are plaintext and html when defining the body key. All other keys are optional and will always fallback to the built-in templates or the template_override_path.

Template Override Path​

email.subject.gotmpl, email.body.gotmpl and email.body.plaintext.gotmpl are common template file names expected in the sub directories of the root directory, corresponding to the respective methods for filling e-mail subject and body. Both plain text and HTML templates are required. The courier uses them as alternatives for fallback.

Creating Templates​

Templates use the golang template engine in the text/template package for rendering the email.subject.gotmpl and email.body.plaintext.gotmpl templates, and the html/template package for rendering the email.body.gotmpl template: https://pkg.go.dev/text/template > https://pkg.go.dev/html/template

Templates can use the Sprig library, which provides more than 100 commonly used template functions: http://masterminds.github.io/sprig/

  • recovery: recovery email templates directory, expected to be located in <root_directory>/recovery
    • valid: sub directory, expected to be located in <template-root>/recovery/valid, containing templates with variables To, RecoveryURL and Identity for validating a recovery
    • invalid: sub directory, expected to be located in <template-root>/recovery/invalid, containing templates with variables To for invalidating a recovery
  • verification: verification email templates directory, expected to be located in <root_directory>/verification
    • valid: sub directory, expected to be located in <template-root>/verification/valid, containing templates with variables To, VerificationURL and Identity for validating a verification
    • invalid: sub directory, expected to be located in <template-root>/verification/invalid, containing templates with variables To for invalidating a verification

For example: https://github.com/ory/kratos/blob/master/courier/template/courier/builtin/templates/verification/valid/email.body.gotmpl

courier/template/templates/verification/valid/email.body.gotmpl
Hi, please verify your account by clicking the following link:

<a href="{{ .VerificationURL }}">{{ .VerificationURL }}</a>
courier/template/templates/verification/valid/email.body.plaintext.gotmpl
Hi, please verify your account by clicking the following link: {{ .VerificationURL }}

If you're running multiple instances of Kratos and separate courier job, make sure to provide templates to all instances (both Kratos and courier).

The Identity attribute​

To be able to customize the content of templates based on the identity of the recipient of the e-mail, the identity has been made available as Identity. This object is a map containing all the attributes of an identity, such as id, state, recovery_addresses, verifiable_addresses and traits.

Nested templates​

You can use nested templates to render email.subject.gotmpl, email.body.gotmpl and email.body.plaintext.gotmpl templates.

Example: i18n customization​

Using nested templates, you can either use in-line template definitions, or as in this example, use separate templates. In this example, we will define the email body for recovery e-mails. Assuming that we've an attribute named lang that contains the required language in the traits of the identity, we can define our templates as indicated below.


{{- if eq .Identity.traits.language "de" -}}
{{ template "email.body.de.gotmpl" . }}
{{- else -}}
{{ template "email.body.en.gotmpl" . }}
{{- end -}}
<a href="{{ .RecoveryURL }}">{{.RecoveryURL }}</a>

Hallo {{ upper .Identity.traits.firstName }},

Um Ihr Konto wiederherzustellen, klicken Sie bitte auf den folgenden Link:


Hello {{ upper .Identity.traits.firstName }},

to recover your account, please click on the link below:

As indicated by the example, we need a root template, which is the email.body.gotmpl template, and then we define sub templates that conform to the following pattern: email.body*. You can also see that the Identity of the user is available in all templates, and that you can use Sprig functions also in the nested templates.

Nested templates with remote templates​

When remote templates are used in Kratos, the dynamics of loading nested templates change. The templates can't reference templates outside itself as with templates loaded from a singular directory.

The template will need to contain the nested templates in the same file. See below for an example.

path/to/my/kratos/config.yml
courier:
  templates:
    verification:
      email:
        body:
          plaintext: https://some-remote-template/tmp.gotmpl
          html: https://some-remote-template/tmp.gotmpl

Our template:

https://some-remote-template/tmp.gotmpl

{{define "en_US"}}
{{ $l := cat "lang=" .lang }}
{{ nospace $l }}
{{end}}

{{- if eq .lang "en_US" -}}
{{ template "en_US" . }}
{{- end -}}