MBL-1168: PKCE class

app/src/main/java/com/kickstarter/libs/utils/CodeVerifier.kt

@@ -0,0 +1,165 @@
+package com.kickstarter.libs.utils
+
+import android.util.Base64
+import timber.log.Timber
+import java.io.UnsupportedEncodingException
+import java.security.MessageDigest
+import java.security.NoSuchAlgorithmException
+import java.security.SecureRandom
+import java.util.regex.Pattern
+
+/**
+ * Generates code verifiers and challenges for PKCE exchange.
+ *
+ * @see [Proof Key for Code Exchange by OAuth Public Clients](https://datatracker.ietf.org/doc/html/rfc7636)
+ */
+class CodeVerifier {
+    companion object {
+        /**
+         * The minimum permitted length for a code verifier.
+         *
+         * @see "Proof Key for Code Exchange by OAuth Public Clients"
+         */
+        const val MIN_CODE_VERIFIER_LENGTH = 43
+
+        /**
+         * The maximum permitted length for a code verifier.
+         *
+         * @see "Proof Key for Code Exchange by OAuth Public Clients"
+         */
+        const val MAX_CODE_VERIFIER_LENGTH = 128
+
+        /**
+         * The default entropy (in bytes) used for the code verifier.
+         */
+        const val DEFAULT_CODE_VERIFIER_ENTROPY = 64
+
+        /**
+         * The minimum permitted entropy (in bytes) for use with
+         * [.generateRandomCodeVerifier].
+         */
+        const val MIN_CODE_VERIFIER_ENTROPY = 32
+
+        /**
+         * The maximum permitted entropy (in bytes) for use with
+         * [.generateRandomCodeVerifier].
+         */
+        const val MAX_CODE_VERIFIER_ENTROPY = 96
+
+        /**
+         * Base64 encoding settings used for generated code verifiers.
+         */
+        private const val PKCE_BASE64_ENCODE_SETTINGS: Int =
+            Base64.NO_WRAP or Base64.NO_PADDING or Base64.URL_SAFE
+
+        /**
+         * Regex for legal code verifier strings, as defined in the spec.
+         *
+         * @see "Proof Key for Code Exchange by OAuth Public Clients"
+         */
+        private val REGEX_CODE_VERIFIER: Pattern =
+            Pattern.compile("^[0-9a-zA-Z\\-._~]{43,128}$")
+
+        /**
+         * SHA-256 based code verifier challenge method.
+         *
+         * @see "Proof Key for Code Exchange by OAuth Public Clients"
+         */
+        const val CODE_CHALLENGE_METHOD_S256 = "S256"
+
+        /**
+         * Plain-text code verifier challenge method. This is only used by AppAuth for Android if
+         * SHA-256 is not supported on this platform.
+         *
+         * @see "Proof Key for Code Exchange by OAuth Public Clients"
+         */
+        const val CODE_CHALLENGE_METHOD_PLAIN = "plain"
+
+        const val ERROR_TOO_SHORT = "codeVerifier length is shorter than allowed by the PKCE specification"
+
+        const val ERROR_TOO_LONG = "codeVerifier length is longer than allowed by the PKCE specification"
+
+        const val ERROR_DO_NOT_MATCH = "codeVerifier string does not match legal code verifier strings REGEX"
+
+        /**
+         * Throws an IllegalArgumentException if the provided code verifier is invalid.
+         *
+         * @see [4.1.  Client Creates a Code Verifier](https://datatracker.ietf.org/doc/html/rfc7636#section-4.1)
+         */
+        fun checkCodeVerifier(codeVerifier: String) {
+            require(
+                MIN_CODE_VERIFIER_LENGTH <= codeVerifier.length
+            ) { ERROR_TOO_SHORT }
+            require(
+                codeVerifier.length <= MAX_CODE_VERIFIER_LENGTH
+            ) { ERROR_TOO_LONG }
+            require(
+                REGEX_CODE_VERIFIER.matcher(codeVerifier).matches()
+            ) { ERROR_DO_NOT_MATCH }
+        }
+
+        /**
+         * Generates a random code verifier string using the provided entropy source and the specified
+         * number of bytes of entropy.
+         */
+        /**
+         * Generates a random code verifier string using [SecureRandom] as the source of
+         * entropy, with the default entropy quantity as defined by
+         * [.DEFAULT_CODE_VERIFIER_ENTROPY].
+         *
+         * @see [Client Creates a Code Verifier](https://datatracker.ietf.org/doc/html/rfc7636#section-4.1)
+         */
+        fun generateRandomCodeVerifier(
+            entropySource: SecureRandom = SecureRandom(),
+            entropyBytes: Int = DEFAULT_CODE_VERIFIER_ENTROPY
+        ): String {
+            require(
+                MIN_CODE_VERIFIER_ENTROPY <= entropyBytes
+            ) { "entropyBytes is less than the minimum permitted" }
+            require(
+                entropyBytes <= MAX_CODE_VERIFIER_ENTROPY
+            ) { "entropyBytes is greater than the maximum permitted" }
+
+            val randomBytes = ByteArray(entropyBytes)
+            entropySource.nextBytes(randomBytes)
+            return Base64.encodeToString(randomBytes, PKCE_BASE64_ENCODE_SETTINGS)
+        }
+
+        /**
+         * Produces a challenge from a code verifier, using SHA-256 as the challenge method if the
+         * system supports it (all Android devices _should_ support SHA-256), and falls back
+         * to the [&quot;plain&quot; challenge type][CODE_CHALLENGE_METHOD_PLAIN] if
+         * unavailable.
+         *
+         * See [Example for the S256 code_challenge_method](https://datatracker.ietf.org/doc/html/rfc7636#appendix-B)
+         */
+        fun generateCodeChallenge(codeVerifier: String): String {
+            return try {
+                val sha256Digester = MessageDigest.getInstance("SHA-256")
+                sha256Digester.update(codeVerifier.toByteArray(charset("ISO_8859_1")))
+                val digestBytes = sha256Digester.digest()
+                Base64.encodeToString(digestBytes, PKCE_BASE64_ENCODE_SETTINGS)
+            } catch (e: NoSuchAlgorithmException) {
+                Timber.w("SHA-256 is not supported on this device! Using plain challenge", e)
+                codeVerifier
+            } catch (e: UnsupportedEncodingException) {
+                Timber.e("ISO-8859-1 encoding not supported on this device!", e)
+                throw IllegalStateException("ISO-8859-1 encoding not supported", e)
+            }
+        }
+
+        private val codeVerifierChallengeMethod: String
+            /**
+             * Returns the challenge method utilized on this system: typically
+             * [SHA-256][CODE_CHALLENGE_METHOD_S256] if supported by
+             * the system, [plain][CODE_CHALLENGE_METHOD_PLAIN] otherwise.
+             */
+            get() = try {
+                MessageDigest.getInstance("SHA-256")
+                // no exception, so SHA-256 is supported
+                CODE_CHALLENGE_METHOD_S256
+            } catch (e: NoSuchAlgorithmException) {
+                CODE_CHALLENGE_METHOD_PLAIN
+            }
+    }
+}

app/src/main/java/com/kickstarter/ui/activities/OAuthActivity.kt

@@ -7,6 +7,7 @@ import android.os.Bundle
 import androidx.appcompat.app.AppCompatActivity
 import androidx.browser.customtabs.CustomTabsIntent
 import androidx.lifecycle.lifecycleScope
+import com.kickstarter.libs.utils.CodeVerifier
 import com.kickstarter.libs.utils.TransitionUtils
 import com.kickstarter.models.chrome.ChromeTabsHelperActivity
 import com.kickstarter.ui.IntentKey
@@ -17,13 +18,21 @@ class OAuthActivity : AppCompatActivity() {
 
     private lateinit var helper: ChromeTabsHelperActivity.CustomTabSessionAndClientHelper
 
+    val redirectUri = "ksrauth2://authorize"
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
 
         setUpConnectivityStatusCheck(lifecycle)
 
-        // TODO MBL-1168 the url will be retrieved from the VM,on MBL-1168 alongside PKCE paramenters
-        val uri = Uri.parse("https://www.kickstarter.com/oauth/authorizations")
+        // TODO: Will be moved to VM all the URI parameters building on MBL-1169
+        val codeVerifier = CodeVerifier.generateRandomCodeVerifier(entropyBytes = CodeVerifier.MAX_CODE_VERIFIER_ENTROPY)
+        val authParams = mapOf(
+            "redirect_uri" to redirectUri,
+            "response_type" to "code",
+            "code_challenge" to CodeVerifier.generateCodeChallenge(codeVerifier), // Set the code challenge
+            "code_challenge_method" to "S256"
+        ).map { (k, v) -> "${(k)}=$v" }.joinToString("&")
+        val uri = Uri.parse("https://www.kickstarter.com/oauth/authorizations?$authParams")
 
         // BindCustomTabsService, obtain CustomTabsClient and Client, listens to navigation events
         helper = ChromeTabsHelperActivity.CustomTabSessionAndClientHelper(this, uri) {

app/src/test/java/com/kickstarter/libs/utils/CodeVerifierTest.kt

@@ -0,0 +1,129 @@
+package com.kickstarter.libs.utils
+
+import com.kickstarter.KSRobolectricTestCase
+import com.kickstarter.libs.utils.CodeVerifier.Companion.ERROR_DO_NOT_MATCH
+import com.kickstarter.libs.utils.CodeVerifier.Companion.ERROR_TOO_LONG
+import com.kickstarter.libs.utils.CodeVerifier.Companion.ERROR_TOO_SHORT
+import com.kickstarter.libs.utils.CodeVerifier.Companion.MAX_CODE_VERIFIER_ENTROPY
+import com.kickstarter.libs.utils.CodeVerifier.Companion.MIN_CODE_VERIFIER_ENTROPY
+import com.kickstarter.libs.utils.CodeVerifier.Companion.generateCodeChallenge
+import com.kickstarter.libs.utils.CodeVerifier.Companion.generateRandomCodeVerifier
+import org.junit.Assert.assertThrows
+import org.junit.Test
+
+class CodeVerifierTest : KSRobolectricTestCase() {
+
+    @Test
+    fun checkCodeVerifier_tooShort_throwsException() {
+        val codeVerifier = createString(CodeVerifier.MIN_CODE_VERIFIER_LENGTH - 1)
+        val exception = assertThrows(IllegalArgumentException::class.java) {
+            CodeVerifier.checkCodeVerifier(codeVerifier)
+        }
+
+        assertEquals(exception.message, ERROR_TOO_SHORT)
+    }
+
+    @Test
+    fun checkCodeVerifier_tooLong_throwsException() {
+        val codeVerifier = createString(CodeVerifier.MAX_CODE_VERIFIER_LENGTH + 1)
+        val exception = assertThrows(IllegalArgumentException::class.java) {
+            CodeVerifier.checkCodeVerifier(codeVerifier)
+        }
+
+        assertEquals(exception.message, ERROR_TOO_LONG)
+    }
+
+    @Test
+    fun checkCodeVerifier_languageSentence_notValid() {
+        val sentence = "Hello, world. I am a string. Hello, world. I am a string."
+        val exception = assertThrows(IllegalArgumentException::class.java) {
+            CodeVerifier.checkCodeVerifier(sentence)
+        }
+
+        assertEquals(exception.message, ERROR_DO_NOT_MATCH)
+    }
+
+    @Test
+    fun generateRandomCodeVerifier_tooLittleEntropy_throwsException() {
+        val exception = assertThrows(IllegalArgumentException::class.java) {
+            CodeVerifier.generateRandomCodeVerifier(
+                entropyBytes = MIN_CODE_VERIFIER_ENTROPY - 1
+            )
+        }
+        assertEquals(exception.message, "entropyBytes is less than the minimum permitted")
+    }
+
+    @Test
+    fun generateRandomCodeVerifier_tooMuchEntropy_throwsException() {
+        val exception = assertThrows(IllegalArgumentException::class.java) {
+            generateRandomCodeVerifier(
+                entropyBytes = MAX_CODE_VERIFIER_ENTROPY + 1
+            )
+        }
+        assertEquals(exception.message, "entropyBytes is greater than the maximum permitted")
+    }
+
+    /**
+     * Generates random String with @param length
+     */
+    private fun createString(length: Int): String {
+        val strChars = CharArray(length)
+        for (i in strChars.indices) {
+            strChars[i] = 'a'
+        }
+        return String(strChars)
+    }
+
+    @Test
+    fun givenSentence_generateCodeChallengeWithSHA256Hash() {
+        // - Use https://oauth.school/exercise/refresh/ to obtain givenCodeChallenge
+        val givenCodeChallenge = "wcaGQDnzgCSNMKc1Jcg1FCfH-0aNWLexAF8-NyegQqE"
+
+        val givenCodeVerifier = "Hello, world. I am a string."
+        val generatedChallenge = generateCodeChallenge(givenCodeVerifier)
+        assertEquals(givenCodeChallenge, generatedChallenge)
+    }
+
+    @Test
+    fun givenCodeVerifierMinEntropy_generateCodeChallengeWithSHA256Hash() {
+        // - [givenVerifier] generated using generateRandomCodeVerifier(MIN_CODE_VERIFIER_ENTROPY)
+        // - Use https://oauth.school/exercise/refresh/ to obtain [givenCodeChallenge]
+        val givenVerifier = "HaTkldnGaT3PcENU5EAY8rtDDNIikQSvBXFFEYBa3MA"
+        val codeChallenge = generateCodeChallenge(givenVerifier)
+
+        val givenCodeChallenge = "khL4OfhvX-uphctb0gMMmE_O5xNX-MfjMPvHxAbpsZk"
+        assertEquals(codeChallenge, givenCodeChallenge)
+    }
+
+    @Test
+    fun givenCodeVerifierDefaultEntropy_generateCodeChallengeWithSHA256Hash() {
+        // - [givenVerifier] generated using generateRandomCodeVerifier(DEFAULT_CODE_VERIFIER_ENTROPY)
+        // - Use https://oauth.school/exercise/refresh/ to obtain [givenCodeChallenge]
+        val givenVerifier = "BAxigyqguFpLKXnGiqc0iabt-Epr3YL-wJvPL0CfDSTGB45_jOwrSrFa0_T4FK5y9amhhYQAk-Bkr2zpD8Gpxw"
+        val codeChallenge = generateCodeChallenge(givenVerifier)
+
+        val givenCodeChallenge = "DcimCRjKEAmp3cl0mFMc12oCsHfN931jzpot2HCkBNo"
+        assertEquals(codeChallenge, givenCodeChallenge)
+    }
+    @Test
+    fun givenCodeVerifierMaxEntropy_generateCodeChallengeWithSHA256Hash() {
+        // - [givenVerifier] generated using generateRandomCodeVerifier(MAX_CODE_VERIFIER_ENTROPY)
+        // - Use https://oauth.school/exercise/refresh/ to obtain [givenCodeChallenge]
+        val givenVerifier = "YfZIzxXTx7Dc58fLNl2uO6cRzWSevpEPeKSXGBFhN8fisOA3XjV_AF0Buz2ZjYxu7S30j15dlzPCzbtHZEHCqAo94YcaZV4JNfJYWCi1jWavu8UUSdCw9n6Y3dinTRfe"
+        val codeChallenge = generateCodeChallenge(givenVerifier)
+
+        val givenCodeChallenge = "cJXeRcpWhJLlsCD8DG3OLkLtjGF8yip6Hf0Jd560Pgg"
+        assertEquals(codeChallenge, givenCodeChallenge)
+    }
+
+    @Test
+    fun generateSeveralCodeVerifiers_checkDoNotMatch() {
+        val codeVerifierA = generateRandomCodeVerifier()
+        val codeVerifierB = generateRandomCodeVerifier()
+        val codeVerifierD = generateRandomCodeVerifier()
+
+        assertTrue(codeVerifierA != codeVerifierB)
+        assertTrue(codeVerifierA != codeVerifierD)
+        assertTrue(codeVerifierB != codeVerifierD)
+    }
+}