4 files changed, 54 insertions, 6 deletions
diff --git a/packages/browser/src/helpers/base64URLStringToBuffer.ts b/packages/browser/src/helpers/base64URLStringToBuffer.ts
new file mode 100644
index 0000000..baa258f
--- /dev/null
+++ b/packages/browser/src/helpers/base64URLStringToBuffer.ts
@@ -0,0 +1,33 @@
+/**
+ * Convert from a Base64URL-encoded string to an Array Buffer. Best used when converting a
+ * credential ID from a JSON string to an ArrayBuffer, like in allowCredentials or
+ * excludeCredentials
+ *
+ * Helper method to compliment `bufferToBase64URLString`
+ */
+export default function base64URLStringToBuffer(base64URLString: string): ArrayBuffer {
+  // Convert from Base64URL to Base64
+  const base64 = base64URLString.replace(/-/g, '+').replace(/_/g, '/');
+  /**
+   * Pad with '=' until it's a multiple of four
+   * (4 - (85 % 4 = 1) = 3) % 4 = 3 padding
+   * (4 - (86 % 4 = 2) = 2) % 4 = 2 padding
+   * (4 - (87 % 4 = 3) = 1) % 4 = 1 padding
+   * (4 - (88 % 4 = 0) = 4) % 4 = 0 padding
+   */
+  const padLength = (4 - (base64.length % 4)) % 4;
+  const padded = base64.padEnd(base64.length + padLength, '=');
+
+  // Convert to a binary string
+  const binary = atob(padded);
+
+  // Convert binary string to buffer
+  const buffer = new ArrayBuffer(binary.length);
+  const bytes = new Uint8Array(buffer);
+
+  for (let i = 0; i < binary.length; i++) {
+    bytes[i] = binary.charCodeAt(i);
+  }
+
+  return buffer;
+}
diff --git a/packages/browser/src/helpers/toBase64String.test.ts b/packages/browser/src/helpers/bufferToBase64URLString.test.ts
index bbcb11b..bbcb11b 100644
--- a/packages/browser/src/helpers/toBase64String.test.ts
+++ b/packages/browser/src/helpers/bufferToBase64URLString.test.ts
diff --git a/packages/browser/src/helpers/bufferToBase64URLString.ts b/packages/browser/src/helpers/bufferToBase64URLString.ts
new file mode 100644
index 0000000..954f4b0
--- /dev/null
+++ b/packages/browser/src/helpers/bufferToBase64URLString.ts
@@ -0,0 +1,21 @@
+/**
+ * Convert the given array buffer into a Base64URL-encoded string. Ideal for converting various
+ * credential response ArrayBuffers to string for sending back to the server as JSON.
+ *
+ * Helper method to compliment `base64URLStringToBuffer`
+ */
+export default function bufferToBase64URLString(buffer: ArrayBuffer): string {
+  const bytes = new Uint8Array(buffer);
+  let str = '';
+
+  for (const charCode of bytes) {
+    str += String.fromCharCode(charCode);
+  }
+
+  const base64String = btoa(str);
+
+  return base64String
+    .replace(/\+/g, '-')
+    .replace(/\//g, '_')
+    .replace(/=/g, '');
+}
diff --git a/packages/browser/src/helpers/toBase64String.ts b/packages/browser/src/helpers/toBase64String.ts
deleted file mode 100644
index 3178695..0000000
--- a/packages/browser/src/helpers/toBase64String.ts
+++ /dev/null
@@ -1,6 +0,0 @@
-import base64js from 'base64-js';
-
-export default function toBase64String(buffer: ArrayBuffer): string {
-  // TODO: Make sure converting buffer to Uint8Array() is correct
-  return base64js.fromByteArray(new Uint8Array(buffer)).replace(/\+/g, '-').replace(/\//g, '_');
-}