Are there any security concerns with using Base64 for Basic Auth credentials?

Yes, there are significant security concerns. Base64 encoding is not encryption; it's merely an encoding scheme that translates binary data into an ASCII string format suitable for transmission over text-based protocols. Anyone who intercepts the HTTP request can easily decode the Base64 string to reveal the plaintext username and password. Therefore, **Basic Authentication should only ever be used over a secure, encrypted connection (HTTPS/TLS)**. Without HTTPS, it provides no confidentiality and is highly vulnerable to eavesdropping attacks and man-in-the-middle attacks.