Custom JWT Authentication¶
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Overview¶
The Custom JWT authentication provider allows users to authenticate with an authentication system that is independent from MongoDB Realm. The external system must return a signed JSON Web Token that contains a unique ID value for the authenticated user.
Realm uses the JWT to identify your application's users and authenticate their requests but does not impose any restrictions on the external authentication system's requirements or authentication methods. For example, the system could require the user to perform two factor authentication, provide specific credentials, or otherwise identify themself.
Configuration¶
Audience¶
The Audience of a JWT specifies its intended recipient. JWTs
describe their audience in the aud claim. By default, Realm expects
aud to contain the App ID of the Realm app for which the provider
is configured.
If the external authentication system JWT specifies a different aud
value, then you can configure the provider to use that value instead.
Verification Method¶
The Verification Method configures how the provider determines which signing algorithm and signing keys the external authentication system must use to sign each JWT.
You can either manually specify signing keys or specify a JSON Web Key URI.
Manually Specify Signing Keys¶
You can manually configure the signing algorithm and specify one or more signing keys that the external authentication system may use to sign JWTs.
Field | Description |
|---|---|
Signing Algorithm config.signingAlgorithm | The cryptographic method that the external system uses to sign the JWT. Custom authentication supports JWTs signed using any of the following algorithms:
 |
Signing Key secret_config.signingKeys | A list of the names of up to three Secrets that each contain a signing key used by the external authentication system to sign JWTs. Each signing key Secret must be a string with length between 32 and 512 characters.  Warning A Signing Key is a secret key and anyone with the key can issue valid user credentials for your app. Ensure that it's never stored in a publicly accessible location, such as a git repository, message board, or in your code. |
Use a JWK URI¶
Some external authentication systems provide a JSON Web Key Set that describes the signing algorithm and signing keys the system uses to sign JWTs. You can use the JWKS to configure the provider instead of manually specifying the signing algorithm and keys.
Field | Description |
|---|---|
Use JWK URI config.useJWKURI | If true, configures Realm to use a signing algorithm and
signing keys defined in a JWK or
JWKS. The JWKS must be accessible at a
URL that you specify. |
JWK URI config.jwkURI | A URL that hosts a JWK or JWKS that describes the signing method
and signing keys the JWTs should use. The JWKS may specify up to
three signing keys and must use the  |
Metadata Fields¶
Metadata Fields are additional data that describe each user.
Realm determines the value of each metadata field from the value of
some field included in the JWT from the external authentication system.
If you set the name field of a user, then Realm will use that
field as the user's display name. Realm refreshes a user's metadata
whenever they log in and exposes the fields in the data object of the
user object.
Field | Description |
|---|---|
Required required | If true , the metadata field is required for all
users associated with the provider, i.e. the JWT returned by the external system must have a
value assigned to the field designated by Path. |
Path name | The name of a field in the JWT that
contains the value for the metadata field. To specify a field in
an embedded object, use dot notation. |
Field Name field_name | Optional. A name for the field in the user object's |
An external authentication system returns JWTs that include
additional information about each user in the user_data field:
{ "aud": "myapp-abcde", "exp": 1516239022, "sub": "24601", "user_data": { "name": "Jean Valjean", "aliases": [ "Monsieur Madeleine", "Ultime Fauchelevent", "Urbain Fabre" ] } }
To include the values from the user_data field in each user's
user object, you could specify the following
metadata fields:
Path | Field Name |
|---|---|
user_data.name | name |
user_data.aliases | aliases |
We can now access the mapped values directly from the user object, which would resemble the following for the given JWT:
{ "id": "59fdd02846244cdse5369ebf", "type": "normal", "data": { "name": "Jean Valjean", "aliases": [ "Monsieur Madeleine", "Ultime Fauchelevent", "Urbain Fabre" ] }, identities: [ { "id": "24601", "provider_type": "custom-token", "data": { "name": "Jean Valjean", "aliases": [ "Monsieur Madeleine", "Ultime Fauchelevent", "Urbain Fabre" ] }, } ] }
JSON Web Tokens¶
The external authentication system must return a JSON web token that uniquely identifies the authenticated user. JSON web tokens are an industry standard (see RFC 7519) for securely representing claims between two parties. A JWT is a string that consists of three parts: a header, a payload and a signature and has the following form:
<header>.<payload>.<signature>
JWT Header¶
The header portion of the JWT consists of a Base64UrlEncoded
document of the following form:
{ "alg": "HS256", "typ": "JWT" }
Field | Description | ||||||
|---|---|---|---|---|---|---|---|
| Required. A string representing the hashing algorithm being used. Realm supports JWTs encoded with the following algorithms:
| ||||||
| Required. The type of the token. Realm expects a JSON web token
so the value should be "JWT". |
JWT Payload¶
The payload portion of the JWT consists of a Base64UrlEncoded
document of the following form:
{ "aud": "<realm app id>" "sub": "<unique user id>", "exp": <NumericDate>, "iat": <NumericDate>, "nbf": <NumericDate>, ... }
Field | Description |
|---|---|
| Required. The audience of the token.
By default, Realm expects this value to be the App ID of your
Realm app. If your external authentication service
returns a different aud value, you should specify that value
instead. |
| Required. The subject of the token. The value should be a unique
ID for the authenticated user from your custom-built
authentication system. |
| Required. The Expiration date of the token. The value should be a NumericDate number indicating the time at which the token expires. Note Realm will not accept expired authentication tokens. |
| Optional. The "issued at" date of the token . The value
should be a NumericDate number that indicates the time after
which the token is considered valid. This field is functionally
identical to nbf. |
| Optional. The "not before" date of the token. The value should be
a NumericDate number that indicates the time before which the
token is considered invalid. This field is functionally identical
to iat. |
Realm ignores any additional fields in the JWT payload
unless you have mapped them to metadata fields in the
provider configuration. Realm
includes the values of mapped fields in the data
document of the authenticated user's user object.
JWT Signature¶
The signature portion of the JWT is a hash of the encoded
token header and payload. To form the signature,
concatenate the encoded header and payload with a period
and sign the result with the Signing Key
specified in the authentication provider configuration using the hashing
algorithm specified in the "alg" field of the header.
HMACSHA256( base64UrlEncode(header) + "." + base64UrlEncode(payload), signingKey )
Examples¶
For code examples that demonstrate how to register and log in using Custom JWT authentication, see the documentation for the Realm SDKs:
Summary¶
- Custom JWT authentication allows you to identify your application's users via a JSON Web Token issued outside of Realm.
- Realm expects JWT audience values to be the App ID of the Realm app unless otherwise configured in the application.
- Realm can verify JWTs using either manually specified keys and signing algorithms or a JSON Web Key URI.
- You can pass custom user data in your JWT that Realm refreshes whenever the user refreshes their token.