[add] function implementation

app/src/main/java/com/acitelight/aether/service/AuthManager.kt

@@ -0,0 +1,46 @@
+package com.acitelight.aether.service
+
+import android.util.Base64
+import com.acitelight.aether.model.ChallengeResponse
+import kotlinx.coroutines.runBlocking
+import org.bouncycastle.crypto.params.Ed25519PrivateKeyParameters
+import org.bouncycastle.crypto.signers.Ed25519Signer
+import java.security.PrivateKey
+import java.security.Signature
+
+object AuthManager {
+    suspend fun fetchToken(baseUrl: String, username: String, privateKey: String): String? = runBlocking {
+        val api = ApiClient.api
+        var challengeBase64 = ""
+        try{
+            challengeBase64 = api.getChallenge(username).string()
+        }catch (e: Exception)
+        {
+            print(e.message)
+        }
+
+        val signedBase64 = signChallenge(db64(privateKey), db64(challengeBase64))
+
+        return@runBlocking try {
+            api.verifyChallenge(username, ChallengeResponse(response = signedBase64)).string()
+        } catch (e: Exception) {
+            e.printStackTrace()
+            null
+        }
+    }
+
+    fun db64(b64: String): ByteArray {
+        return Base64.decode(b64, Base64.DEFAULT) // 32 bytes
+    }
+
+    fun signChallenge(privateKey: ByteArray, data: ByteArray): String
+    {
+        val privateKeyParams = Ed25519PrivateKeyParameters(privateKey, 0)
+        val signer = Ed25519Signer()
+        signer.init(true, privateKeyParams)
+
+        signer.update(data, 0, data.size)
+        val signature = signer.generateSignature()
+        return Base64.encodeToString(signature, Base64.NO_WRAP)
+    }
+}