add PrivateKeyProvider

.editorconfig

@@ -17,6 +17,10 @@ tab_width = 2
 [*.bat]
 end_of_line = crlf
 
+[*.pem]
+max_line_length = 64
+insert_final_newline = false
+
 # noinspection EditorConfigKeyCorrectness
 [*.{kt,kts}]
 ij_kotlin_packages_to_use_import_on_demand = unset

src/main/kotlin/ltd/hlaeja/exception/KeyProviderException.kt

@@ -0,0 +1,23 @@
+package ltd.hlaeja.exception
+
+@Suppress("unused")
+class KeyProviderException : RuntimeException {
+
+    constructor() : super()
+
+    constructor(message: String) : super(message)
+
+    constructor(cause: Throwable) : super(cause)
+
+    constructor(
+        message: String,
+        cause: Throwable,
+    ) : super(message, cause)
+
+    constructor(
+        message: String,
+        cause: Throwable,
+        enableSuppression: Boolean,
+        writableStackTrace: Boolean,
+    ) : super(message, cause, enableSuppression, writableStackTrace)
+}

src/main/kotlin/ltd/hlaeja/util/PrivateKeyProvider.kt

@@ -0,0 +1,35 @@
+package ltd.hlaeja.util
+
+import java.security.KeyFactory
+import java.security.interfaces.RSAPrivateKey
+import java.security.spec.PKCS8EncodedKeySpec
+import java.util.Base64.getDecoder
+import ltd.hlaeja.exception.KeyProviderException
+
+object PrivateKeyProvider {
+
+    fun load(
+        pemFile: String,
+    ): RSAPrivateKey = readPrivatePemFile(pemFile)
+        .let(::makePrivateKey)
+
+    private fun makePrivateKey(
+        privateKeyBytes: ByteArray,
+    ): RSAPrivateKey = KeyFactory.getInstance("RSA")
+        .generatePrivate(PKCS8EncodedKeySpec(privateKeyBytes)) as RSAPrivateKey
+
+    private fun readPrivatePemFile(
+        privateKey: String,
+    ): ByteArray = javaClass.classLoader
+        .getResource(privateKey)
+        ?.readText()
+        ?.let(::getPrivateKeyByteArray)
+        ?: throw KeyProviderException("Could not load private key")
+
+    private fun getPrivateKeyByteArray(
+        keyText: String,
+    ): ByteArray = keyText.replace(Regex("[\r\n]+"), "")
+        .removePrefix("-----BEGIN PRIVATE KEY-----")
+        .removeSuffix("-----END PRIVATE KEY-----")
+        .let { getDecoder().decode(it) }
+}

src/test/kotlin/ltd/hlaeja/util/PrivateKeyProviderTest.kt

@@ -0,0 +1,51 @@
+package ltd.hlaeja.util
+
+import java.security.interfaces.RSAPrivateKey
+import ltd.hlaeja.exception.KeyProviderException
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
+
+class PrivateKeyProviderTest {
+
+    @Test
+    fun `load private key - success`() {
+        // given
+        val pemFilePath = "keys/valid-private-key.pem"
+
+        // when
+        val privateKey: RSAPrivateKey = PrivateKeyProvider.load(pemFilePath)
+
+        // then
+        assertThat(privateKey).isNotNull
+        assertThat(privateKey.algorithm).isEqualTo("RSA")
+    }
+
+    @Test
+    fun `load private key - file does not exist`() {
+        // given
+        val nonExistentPemFilePath = "keys/non-existent.pem"
+
+        // when exception
+        val exception = assertThrows<KeyProviderException> {
+            PrivateKeyProvider.load(nonExistentPemFilePath)
+        }
+
+        // then
+        assertThat(exception.message).isEqualTo("Could not load private key")
+    }
+
+    @Test
+    fun `load private key - file is invalid`() {
+        // given
+        val invalidPemFilePath = "keys/invalid-private-key.pem"
+
+        // when exception
+        val exception = assertThrows<IllegalArgumentException> {
+            PrivateKeyProvider.load(invalidPemFilePath)
+        }
+
+        // then
+        assertThat(exception.message).contains("Input byte array has wrong 4-byte ending unit")
+    }
+}

src/test/resources/keys/invalid-private-key.pem

@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----
+VEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBK
+VU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMg
+SVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBU
+SElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpV
+TksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJ
+UyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRI
+SVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVO
+SyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElT
+IEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJ
+UyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5L
+IFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMg
+SlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElT
+IElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksg
+VEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBK
+VU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMg
+SVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBU
+SElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpV
+TksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJ
+UyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRI
+SVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVO
+SyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElT
+IEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJ
+UyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5L
+IFRISVMgSVMgSlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMg
+SlVOSyBUSElTIElTIEpVTksgVEhJUyBJUyBKVU5LIFRISVMgSVMgSlVOSyBUSElT
+IElTIEpVTksg==
+-----END PRIVATE KEY-----

src/test/resources/keys/valid-private-key.pem

@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----
+MIIEvwIBADANBgkqhkiG9w0BAQEFAASCBKkwggSlAgEAAoIBAQC7VJTUt9Us8cKj
+MzEfYyjiWA4R4/M2bS1GB4t7NXp98C3SC6dVMvDuictGeurT8jNbvJZHtCSuYEvu
+NMoSfm76oqFvAp8Gy0iz5sxjZmSnXyCdPEovGhLa0VzMaQ8s+CLOyS56YyCFGeJZ
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+VuNd9tybAgMBAAECggEBAKTmjaS6tkK8BlPXClTQ2vpz/N6uxDeS35mXpqasqskV
+laAidgg/sWqpjXDbXr93otIMLlWsM+X0CqMDgSXKejLS2jx4GDjI1ZTXg++0AMJ8
+sJ74pWzVDOfmCEQ/7wXs3+cbnXhKriO8Z036q92Qc1+N87SI38nkGa0ABH9CN83H
+mQqt4fB7UdHzuIRe/me2PGhIq5ZBzj6h3BpoPGzEP+x3l9YmK8t/1cN0pqI+dQwY
+dgfGjackLu/2qH80MCF7IyQaseZUOJyKrCLtSD/Iixv/hzDEUPfOCjFDgTpzf3cw
+ta8+oE4wHCo1iI1/4TlPkwmXx4qSXtmw4aQPz7IDQvECgYEA8KNThCO2gsC2I9PQ
+DM/8Cw0O983WCDY+oi+7JPiNAJwv5DYBqEZB1QYdj06YD16XlC/HAZMsMku1na2T
+N0driwenQQWzoev3g2S7gRDoS/FCJSI3jJ+kjgtaA7Qmzlgk1TxODN+G1H91HW7t
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+48RakUKClU8CgYEAzV7W3COOlDDcQd935DdtKBFRAPRPAlspQUnzMi5eSHMD/ISL
+DY5IiQHbIH83D4bvXq0X7qQoSBSNP7Dvv3HYuqMhf0DaegrlBuJllFVVq9qPVRnK
+xt1Il2HgxOBvbhOT+9in1BzA+YJ99UzC85O0Qz06A+CmtHEy4aZ2kj5hHjECgYEA
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+VBIovic5l0xFkEHskAjFTevO86Fsz1C2aSeRKSqGFoOQ0tmJzBEs1R6KqnHInicD
+TQrKhArgLXX4v3CddjfTRJkFWDbE/CkvKZNOrcf1nhaGCPspRJj2KUkj1Fhl9Cnc
+dn/RsYEONbwQSjIfMPkvxF+8HQ==
+-----END PRIVATE KEY-----