diff --git a/packages/http-client/src/index.ts b/packages/http-client/src/index.ts
index 6f575f7d13..6ee9ae43a5 100644
--- a/packages/http-client/src/index.ts
+++ b/packages/http-client/src/index.ts
@@ -726,7 +726,9 @@ export class HttpClient {
       uri: proxyUrl.href,
       pipelining: !this._keepAlive ? 0 : 1,
       ...((proxyUrl.username || proxyUrl.password) && {
-        token: `${proxyUrl.username}:${proxyUrl.password}`
+        token: `Basic ${Buffer.from(
+          `${proxyUrl.username}:${proxyUrl.password}`
+        ).toString('base64')}`
       })
     })
     this._proxyAgentDispatcher = proxyAgent