Scripts should extend ResourceContainer and should be stored in JCR as a node of type exo:groovyResourceContainer.

Detailed REST services step-by-step implementation check there Create REST service step by step.

Component configuration enables Groovy services loader:

<component>

  <type>org.exoplatform.services.jcr.ext.script.groovy.GroovyScript2RestLoader</type>

  <init-params>

    <object-param>

      <name>observation.config</name>

      <object type="org.exoplatform.services.jcr.ext.script.groovy.GroovyScript2RestLoader$ObservationListenerConfiguration">

        <field name="repository">

          <string>repository</string>

        </field>

        <field name="workspaces">

          <collection type="java.util.ArrayList">

            <value>

              <string>collaboration</string>

            </value>

          </collection>

        </field>

      </object>

    </object-param>

  </init-params>

</component>