Cedarling Kotlin binding#

UniFFI (Universal Foreign Function Interface) is a tool developed by Mozilla to simplify cross-language bindings, primarily between Rust and other languages like Kotlin, Swift, and Python. It allows Rust libraries to be used in these languages without manually writing complex foreign function interface (FFI) bindings.

Please refer to this document for details on the structs, enums, and functions exposed by UniFFI bindings. This section outlines the process of generating the Kotlin binding for Cedarling using Cedarling UniFFI. The Kotlin binding is then wrapped in a Java class to enable convenient use in Java applications.

Prerequisites#

Rust: Install it from the official Rust website.
Java Development Kit (JDK): version 21 or higher
Apache Maven: Install it from Apache Maven Website

Building from Source#

Build Cedarling by executing below command from ./jans/jans-cedarling of cloned jans project:
```
cargo build -r -p cedarling_uniffi
```
In target/release, you should find the libcedarling_uniffi.dylib (if Mac OS), libcedarling_uniffi.so (if Linux OS), or libcedarling_uniffi.dll (if Windows OS) file, depending on the operating system you are using.
Generate the bindings for Kotlin by running the command below. Replace {build_file} with libcedarling_uniffi.dylib, libcedarling_uniffi.so, or libcedarling_uniffi.dll, depending on which file is generated in target/release.
```
cargo run --bin uniffi-bindgen generate --library ./target/release/{build_file} --language kotlin --out-dir ./bindings/cedarling-java/src/main/kotlin/io/jans/cedarling
```
Copy the generated libcedarling_uniffi.dylib, libcedarling_uniffi.so, or libcedarling_uniffi.dll file to resource directory of the cedarling-java Maven project. Replace {build_file} in the below commad with libcedarling_uniffi.dylib, libcedarling_uniffi.so, or libcedarling_uniffi.dll, depending on which file is generated in target/release.
```
mkdir ./bindings/cedarling-java/src/main/resources
cp ./target/release/{build_file} ./bindings/cedarling-java/src/main/resources
```
Change directory to ./bindings/cedarling-java and run below command to build cedarling-java jar file. This will generate cedarling-java-{version}-distribution.jar at ./bindings/cedarling-java/target/.
```
 mvn clean install
```

Recipes#

Recipe 1: Using the Cedarling Java binding in custom scripts on the Janssen Auth Server (VM installation).#

Note: This recipe is compatible with Jans version 1.4.0 and earlier.

Upload bootstrap.json, policy-store.json, action.txt, context.json, principals.json and resource.json at /opt/jans/jetty/jans-auth/custom/static location of the auth server. The Asset Screen can be used to upload assets.
Upload the generate cedarling-java-{version}-distribution.jar at /opt/jans/jetty/jans-auth/custom/libs location of the auth server.
The following Post Authn script has been created for calling Cedarling authorization. Add and enable the Post Authn custom script (in Java) with following Custom Properties:

Key	Values
BOOTSTRAP_JSON_PATH	./custom/static/bootstrap.json
ACTION_FILE_PATH	./custom/static/action.txt
RESOURCE_FILE_PATH	./custom/static/resource.json
CONTEXT_FILE_PATH	./custom/static/context.json
PRINCIPALS_FILE_PATH	./custom/static/principals.json

Map the script with client used to perform authentication.
The script runs after client authentication to invoke Cedarling authz.

Recipe 2: Sample Java Maven project using the Kotlin binding#

Build Cedarling:
```
cargo build -r -p cedarling_uniffi
```
In target/release, you should find the libcedarling_uniffi.dylib (if Mac OS), libcedarling_uniffi.so (if Linux OS), or libcedarling_uniffi.dll (if Windows OS) file, depending on the operating system you are using.
Generate the bindings for Kotlin by running the command below. Replace {build_file} with libcedarling_uniffi.dylib, libcedarling_uniffi.so, or libcedarling_uniffi.dll, depending on which file is generated in target/release.
```
cargo run --bin uniffi-bindgen generate --library ./target/release/{build_file} --language kotlin --out-dir ./bindings/cedarling_uniffi/javaApp/src/main/kotlin/org/example
```
Copy the generated libcedarling_uniffi.dylib, libcedarling_uniffi.so, or libcedarling_uniffi.dll file to resource directory of the sample Java Maven project. Replace {build_file} in the below commad with libcedarling_uniffi.dylib, libcedarling_uniffi.so, or libcedarling_uniffi.dll, depending on which file is generated in target/release.
```
cp ./target/release/{build_file} ./bindings/cedarling_uniffi/javaApp/src/main/resources
```
Change directory to sample Java project (./bindings/cedarling_uniffi/javaApp) and run below command to run the main method of a Maven project from the terminal.
```
 mvn clean install
 mvn exec:java -Dexec.mainClass="org.example.Main"
```
The method will execute the steps for Cedarling initialization with a sample bootstrap configuration, run authorization with sample tokens, resource and context inputs and call log interface to print authorization logs on console.

Sample Java Maven Project#

Note the following points in the sample Java Maven project to understand the changes required for using the Kotlin binding in other Java projects.

The sample tokens, resource and context input files along with files containing bootstrap configuration and policy- store used by the sample application are present at ./bindings/cedarling_uniffi/javaApp/src/main/resources/config.
Refer to the Java code in org.example.Main to see how Cedarling's init, authz, and log interfaces are called using the Kotlin binding.

Added dependencies in pom.xml:#

Java Native Access (JNA): A Java library that allows Java code to call native shared libraries (like .so on Linux, .dll on Windows, or .dylib on macOS) without writing JNI (Java Native Interface) code.
kotlinx.coroutines: Adds support for asynchronous programming using coroutines.
kotlin-stdlib-jdk: The kotlin-stdlib-jdk8 library is a variant of the Kotlin standard library that includes additional features specifically designed to work with JDK 8 (Java Development Kit 8) or higher.
nimbus-jose-jwt: The nimbus-jose-jwt library is a Java library used for working with JWTs (JSON Web Tokens) and JOSE (JavaScript Object Signing and Encryption) standards
jackson-databind: The jackson-databind library is a core module of the Jackson JSON processing framework in Java

Last update: 2025-05-29
Created: 2025-05-13