From f6dc766910b3b38777c3e2e4e20349b5e01e0877 Mon Sep 17 00:00:00 2001
From: Swordsteel <swordsteel@gmail.com>
Date: Wed, 1 Jan 2025 01:09:14 +0100
Subject: [PATCH] add PublicKeyProvider

---
 .../ltd/hlaeja/jwt/util/PublicKeyProvider.kt  | 35 +++++++++++++
 .../hlaeja/jwt/util/PublicKeyProviderTest.kt  | 50 +++++++++++++++++++
 2 files changed, 85 insertions(+)
 create mode 100644 src/main/kotlin/ltd/hlaeja/jwt/util/PublicKeyProvider.kt
 create mode 100644 src/test/kotlin/ltd/hlaeja/jwt/util/PublicKeyProviderTest.kt

diff --git a/src/main/kotlin/ltd/hlaeja/jwt/util/PublicKeyProvider.kt b/src/main/kotlin/ltd/hlaeja/jwt/util/PublicKeyProvider.kt
new file mode 100644
index 0000000..52fec03
--- /dev/null
+++ b/src/main/kotlin/ltd/hlaeja/jwt/util/PublicKeyProvider.kt
@@ -0,0 +1,35 @@
+package ltd.hlaeja.jwt.util
+
+import java.security.KeyException
+import java.security.KeyFactory
+import java.security.interfaces.RSAPublicKey
+import java.security.spec.X509EncodedKeySpec
+import java.util.Base64.getDecoder
+
+object PublicKeyProvider {
+
+    fun load(
+        pemFile: String,
+    ): RSAPublicKey = readPublicPemFile(pemFile)
+        .let(PublicKeyProvider::makePublicKey)
+
+    private fun makePublicKey(
+        publicKeyBytes: ByteArray,
+    ): RSAPublicKey = KeyFactory.getInstance("RSA")
+        .generatePublic(X509EncodedKeySpec(publicKeyBytes)) as RSAPublicKey
+
+    private fun readPublicPemFile(
+        publicKey: String,
+    ): ByteArray = javaClass.classLoader
+        ?.getResource(publicKey)
+        ?.readText()
+        ?.let(PublicKeyProvider::getPublicKeyByteArray)
+        ?: throw KeyException("Could not load public key")
+
+    private fun getPublicKeyByteArray(
+        keyText: String,
+    ): ByteArray = keyText.replace(Regex("[\r\n]+"), "")
+        .removePrefix("-----BEGIN PUBLIC KEY-----")
+        .removeSuffix("-----END PUBLIC KEY-----")
+        .let { getDecoder().decode(it) }
+}
diff --git a/src/test/kotlin/ltd/hlaeja/jwt/util/PublicKeyProviderTest.kt b/src/test/kotlin/ltd/hlaeja/jwt/util/PublicKeyProviderTest.kt
new file mode 100644
index 0000000..4fa0b30
--- /dev/null
+++ b/src/test/kotlin/ltd/hlaeja/jwt/util/PublicKeyProviderTest.kt
@@ -0,0 +1,50 @@
+package ltd.hlaeja.jwt.util
+
+import java.security.KeyException
+import java.security.interfaces.RSAPublicKey
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+
+class PublicKeyProviderTest {
+
+    @Test
+    fun `load public key - success`() {
+        // given
+        val pemFilePath = "cert/valid-public-key.pem"
+
+        // when
+        val publicKey: RSAPublicKey = PublicKeyProvider.load(pemFilePath)
+
+        // then
+        assertThat(publicKey).isNotNull
+        assertThat(publicKey.algorithm).isEqualTo("RSA")
+    }
+
+    @Test
+    fun `load public key - file does not exist`() {
+        // given
+        val nonExistentPemFilePath = "cert/non-existent.pem"
+
+        // when exception
+        val exception = org.junit.jupiter.api.assertThrows<KeyException> {
+            PublicKeyProvider.load(nonExistentPemFilePath)
+        }
+
+        // then
+        assertThat(exception.message).isEqualTo("Could not load public key")
+    }
+
+    @Test
+    fun `load public key - file is invalid`() {
+        // given
+        val invalidPemFilePath = "cert/invalid-public-key.pem"
+
+        // when exception
+        val exception = org.junit.jupiter.api.assertThrows<IllegalArgumentException> {
+            PrivateKeyProvider.load(invalidPemFilePath)
+        }
+
+        // then
+        assertThat(exception.message).contains("Illegal base64 character 2d")
+    }
+}