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By default, the plugin generates JWT tokens. Note that when using JWT, you can't plug any other token generator. For
more information about how this plugin uses JWT's, check the <<tokenStorage>> section.

=== JWT

==== Claims

It is possible, to include additional claims in the JWT generated. To do so, you can plug one or more implementations of the interface
{baseGroovyApiUrl}grails/plugin/springsecurity/rest/token/generation/jwt/CustomClaimProvider.html[CustomClaimProvider],
and register them in Spring.

The plugin comes prepackaged with a
{baseGroovyApiUrl}grails/plugin/springsecurity/rest/token/generation/jwt/IssuerClaimProvider.html[IssuerClaimProvider],
that sets the `iss` field of the JWT claim set, and which value is configurable using the following configuration property:
`grails.plugin.springsecurity.rest.token.generation.jwt.issuer`.

Customising the JWT to include additional claims is a piece of cake. First, create the claim provider:

[source,groovy]
----
class BookListClaimProvider implements CustomClaimProvider {

    @Override
    void provideCustomClaims(JWTClaimsSet.Builder builder, UserDetails details, String principal, Integer expiration) {
        builder.claim('books', Book.findAllByAuthor(details.username).collect { it.name })
    }

}
----

Then, register it in Spring via `resources.groovy`, or using the `@Bean` annotation in a method of the `Application` class
(or any `@Configuration` class):

[source,groovy]
----
@Bean
CustomClaimProvider bookListClaimProvider() {
    new BookListClaimProvider()
}
----

==== Algorithms

This plugin uses http://connect2id.com/products/nimbus-jose-jwt[Nimbus JOSE+JWT] library to generate and parse JWT's,
and the signing / encryption algorithms are configurable, as long as they are supported in Nimbus.

If using signed JWT's, the relevant configuration is the following:

.Signed JWT configuration options
|===
| *Config key*  | *Possible values* | *Default value*

|`grails.plugin.springsecurity.rest.token.generation.jwt.algorithm`
|Any http://static.javadoc.io/com.nimbusds/nimbus-jose-jwt/4.26.1/com/nimbusds/jose/JWSAlgorithm.html[`JWSAlgorithm`]
|`HS256`

|`grails.plugin.springsecurity.rest.token.storage.jwt.secret`
|At least 256 bits (32 characters)
|`null`
|===

When using encrypted JWT's, those are the possible configuration options:

.Encrypted JWT configuration options
|===
| *Config key*  | *Possible values* | *Default value*

|`grails.plugin.springsecurity.rest.token.generation.jwt.jweAlgorithm`
|Any http://static.javadoc.io/com.nimbusds/nimbus-jose-jwt/4.26.1/com/nimbusds/jose/JWEAlgorithm.html[`JWEAlgorithm`]
|`RSA-OAEP`

|`grails.plugin.springsecurity.rest.token.generation.jwt.encryptionMethod`
|Any http://static.javadoc.io/com.nimbusds/nimbus-jose-jwt/4.26.1/com/nimbusds/jose/EncryptionMethod.html[`EncryptionMethod`]
|`A128GCM`
|===



=== Memcached, GORM, Redis, Grails Cache

If you are not using JWT, but any stateful strategy like Memcached or GORM, the following strategies are available:

* {baseGroovyApiUrl}grails/plugin/springsecurity/rest/token/generation/SecureRandomTokenGenerator.html[Using java.security.SecureRandom].
* {baseGroovyApiUrl}grails/plugin/springsecurity/rest/token/generation/UUIDTokenGenerator.html[Using java.util.UUID].

The strategy used is configurable:

.Token generation configuration options
[cols="80,20"]
|===
| *Config key*  | *Default value*

|`grails.plugin.springsecurity.rest.token.generation.useSecureRandom`
|`true`

|`grails.plugin.springsecurity.rest.token.generation.useUUID`
|`false`
|===

Both of them generate tokens of 32 alphanumeric characters.

That should be enough for most of the human beings. But if you still want to provide your own implementation,
simply write a class implementing
include::{baseGroovyApiUrl}grails/plugin/springsecurity/rest/token/generation/TokenGenerator.html[TokenGenerator]
and wire it up in `resources.groovy` as `tokenGenerator`.
