diff --git a/packages/client-core/lib/Client.js b/packages/client-core/lib/Client.js
index bd9a18a7..b0bdcbc3 100644
--- a/packages/client-core/lib/Client.js
+++ b/packages/client-core/lib/Client.js
@@ -47,7 +47,7 @@ class Client extends Connection {
     // after the confidentiality and integrity of the stream are protected via TLS
     // or an equivalent security layer.
     // https://xmpp.org/rfcs/rfc6120.html#rfc.section.4.7.1
-    const from = this.socket?.isSecure() && this.jid?.bare().toString();
+    const from = this.isSecure() && this.jid?.bare().toString();
     if (from) headerElement.attrs.from = from;
     return this.Transport.prototype.header(headerElement, ...args);
   }
diff --git a/packages/client-core/test/Client.js b/packages/client-core/test/Client.js
index e510e9cb..77913608 100644
--- a/packages/client-core/test/Client.js
+++ b/packages/client-core/test/Client.js
@@ -32,21 +32,20 @@ test("header", () => {
 
   const entity = new Client();
   entity.Transport = Transport;
-  entity.socket = {};
 
   entity.jid = null;
-  entity.socket.isSecure = () => false;
+  entity.isSecure = () => false;
   expect(entity.header(<foo />)).toEqual(<foo />);
 
   entity.jid = null;
-  entity.socket.isSecure = () => true;
+  entity.isSecure = () => true;
   expect(entity.header(<foo />)).toEqual(<foo />);
 
   entity.jid = new JID("foo@bar/example");
-  entity.socket.isSecure = () => false;
+  entity.isSecure = () => false;
   expect(entity.header(<foo />)).toEqual(<foo />);
 
   entity.jid = new JID("foo@bar/example");
-  entity.socket.isSecure = () => true;
+  entity.isSecure = () => true;
   expect(entity.header(<foo />)).toEqual(<foo from="foo@bar" />);
 });
diff --git a/packages/client/README.md b/packages/client/README.md
index 2ac26d1f..f3a61d35 100644
--- a/packages/client/README.md
+++ b/packages/client/README.md
@@ -265,6 +265,21 @@ Returns a promise that resolves once all the stanzas have been sent.
 
 If you need to send a stanza to multiple recipients we recommend using [Extended Stanza Addressing](https://xmpp.org/extensions/xep-0033.html) instead.
 
+### isSecure
+
+Returns whether the connection is considered secured.
+
+```js
+console.log(xmpp.isSecure());
+```
+
+Considered secure:
+
+- localhost, 127.0.0.1, ::1
+- encrypted channels (wss, xmpps, starttls)
+
+This method returns false if there is no connection.
+
 ### xmpp.reconnect
 
 See [@xmpp/reconnect](/packages/reconnect).
diff --git a/packages/client/lib/createOnAuthenticate.js b/packages/client/lib/createOnAuthenticate.js
index 907a180b..8d8c4ea1 100644
--- a/packages/client/lib/createOnAuthenticate.js
+++ b/packages/client/lib/createOnAuthenticate.js
@@ -1,23 +1,31 @@
 const ANONYMOUS = "ANONYMOUS";
+const PLAIN = "PLAIN";
 
 export default function createOnAuthenticate(credentials, userAgent) {
-  return async function onAuthenticate(authenticate, mechanisms, fast) {
+  return async function onAuthenticate(authenticate, mechanisms, fast, entity) {
     if (typeof credentials === "function") {
       await credentials(authenticate, mechanisms, fast);
       return;
     }
 
-    if (
-      !credentials?.username &&
-      !credentials?.password &&
-      mechanisms.includes(ANONYMOUS)
-    ) {
-      await authenticate(credentials, ANONYMOUS, userAgent);
-      return;
-    }
+    credentials.token ??= await fast?.fetch();
 
-    credentials.token = await fast?.fetch?.();
-
-    await authenticate(credentials, mechanisms[0], userAgent);
+    const mechanism = getMechanism({ mechanisms, entity, credentials });
+    await authenticate(credentials, mechanism, userAgent);
   };
 }
+
+export function getMechanism({ mechanisms, entity, credentials }) {
+  if (
+    !credentials?.username &&
+    !credentials?.password &&
+    !credentials?.token &&
+    mechanisms.includes(ANONYMOUS)
+  ) {
+    return ANONYMOUS;
+  }
+
+  if (entity.isSecure()) return mechanisms[0];
+
+  return mechanisms.find((mechanism) => mechanism !== PLAIN);
+}
diff --git a/packages/client/test/getMechanism.js b/packages/client/test/getMechanism.js
new file mode 100644
index 00000000..36deac0d
--- /dev/null
+++ b/packages/client/test/getMechanism.js
@@ -0,0 +1,38 @@
+import { getMechanism } from "../lib/createOnAuthenticate.js";
+
+it("returns ANONYMOUS if available and there are no credentials", () => {
+  expect(
+    getMechanism({
+      credentials: {},
+      mechanisms: ["PLAIN", "ANONYMOUS"],
+    }),
+  ).toBe("ANONYMOUS");
+});
+
+it("returns the first mechanism if the connection is secure", () => {
+  expect(
+    getMechanism({
+      credentials: { username: "foo", password: "bar" },
+      mechanisms: ["PLAIN", "SCRAM-SHA-1"],
+      entity: { isSecure: () => true },
+    }),
+  ).toBe("PLAIN");
+});
+
+it("does not return PLAIN if the connection is not secure", () => {
+  expect(
+    getMechanism({
+      credentials: { username: "foo", password: "bar" },
+      mechanisms: ["PLAIN", "SCRAM-SHA-1"],
+      entity: { isSecure: () => false },
+    }),
+  ).toBe("SCRAM-SHA-1");
+
+  expect(
+    getMechanism({
+      credentials: { username: "foo", password: "bar" },
+      mechanisms: ["PLAIN"],
+      entity: { isSecure: () => false },
+    }),
+  ).toBe(undefined);
+});
diff --git a/packages/connection/index.js b/packages/connection/index.js
index 93c4d3c7..e641b133 100644
--- a/packages/connection/index.js
+++ b/packages/connection/index.js
@@ -22,6 +22,10 @@ class Connection extends EventEmitter {
     this.root = null;
   }
 
+  isSecure() {
+    return !!this.socket?.isSecure();
+  }
+
   async _streamError(condition, children) {
     try {
       await this.send(
diff --git a/packages/connection/test/isSecure.js b/packages/connection/test/isSecure.js
new file mode 100644
index 00000000..e76571d5
--- /dev/null
+++ b/packages/connection/test/isSecure.js
@@ -0,0 +1,14 @@
+import Connection from "../index.js";
+
+test("isSecure()", () => {
+  const conn = new Connection();
+
+  conn.socket = null;
+  expect(conn.isSecure()).toBe(false);
+
+  conn.socket = { isSecure: () => false };
+  expect(conn.isSecure()).toBe(false);
+
+  conn.socket = { isSecure: () => true };
+  expect(conn.isSecure()).toBe(true);
+});
diff --git a/packages/sasl/index.js b/packages/sasl/index.js
index 7c47312a..0fad0407 100644
--- a/packages/sasl/index.js
+++ b/packages/sasl/index.js
@@ -84,7 +84,7 @@ export default function sasl({ streamFeatures, saslFactory }, onAuthenticate) {
       });
     }
 
-    await onAuthenticate(done, mechanisms);
+    await onAuthenticate(done, mechanisms, null, entity);
 
     await entity.restart();
   });
diff --git a/packages/sasl2/index.js b/packages/sasl2/index.js
index d81ddfed..f6d2c86a 100644
--- a/packages/sasl2/index.js
+++ b/packages/sasl2/index.js
@@ -106,7 +106,12 @@ export default function sasl2({ streamFeatures, saslFactory }, onAuthenticate) {
         throw new SASLError("SASL: No compatible mechanism available.");
       }
 
-      await onAuthenticate(done, mechanisms, fast_available && fast);
+      await onAuthenticate(
+        done,
+        mechanisms,
+        fast_available ? fast : null,
+        entity,
+      );
 
       async function done(credentials, mechanism, userAgent) {
         if (fast_available) {
diff --git a/packages/test/mockSocket.js b/packages/test/mockSocket.js
index 09f25c72..5bb0c455 100644
--- a/packages/test/mockSocket.js
+++ b/packages/test/mockSocket.js
@@ -6,6 +6,9 @@ class MockSocket extends net.Socket {
       cb?.();
     });
   }
+  isSecure() {
+    return true;
+  }
 }
 
 export default function mockSocket() {
diff --git a/rollup.config.js b/rollup.config.js
index fd709d68..8e905d2c 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -14,6 +14,7 @@ export default [
       name: "XMPP",
     },
     plugins: [
+      terser(),
       babel({ babelHelpers: "runtime" }),
       nodePolyfills(),
       nodeResolve({ preferBuiltins: false, browser: true }),