diff --git a/packages/core/src/auth.ts b/packages/core/src/auth.ts
index bc036743..fbef599a 100644
--- a/packages/core/src/auth.ts
+++ b/packages/core/src/auth.ts
@@ -21,6 +21,7 @@ import {
   sendSignInLinkToEmail as _sendSignInLinkToEmail,
   signInAnonymously as _signInAnonymously,
   signInWithPhoneNumber as _signInWithPhoneNumber,
+  signInWithCredential as _signInWithCredential,
   ActionCodeSettings,
   ApplicationVerifier,
   AuthProvider,
@@ -28,8 +29,6 @@ import {
   EmailAuthProvider,
   linkWithCredential,
   PhoneAuthProvider,
-  signInWithCredential,
-  signInWithRedirect,
   UserCredential,
 } from "firebase/auth";
 import { getBehavior, hasBehavior } from "./behaviors";
@@ -70,7 +69,7 @@ export async function signInWithEmailAndPassword(
     }
 
     ui.setState("pending");
-    const result = await signInWithCredential(ui.auth, credential);
+    const result = await _signInWithCredential(ui.auth, credential);
     return handlePendingCredential(ui, result);
   } catch (error) {
     handleFirebaseError(ui, error);
@@ -138,7 +137,7 @@ export async function confirmPhoneNumber(
     }
 
     ui.setState("pending");
-    const result = await signInWithCredential(ui.auth, credential);
+    const result = await _signInWithCredential(ui.auth, credential);
     return handlePendingCredential(ui, result);
   } catch (error) {
     handleFirebaseError(ui, error);
@@ -193,7 +192,7 @@ export async function signInWithEmailLink(
     }
 
     ui.setState("pending");
-    const result = await signInWithCredential(ui.auth, credential);
+    const result = await _signInWithCredential(ui.auth, credential);
     return handlePendingCredential(ui, result);
   } catch (error) {
     handleFirebaseError(ui, error);
@@ -214,20 +213,21 @@ export async function signInAnonymously(ui: FirebaseUIConfiguration): Promise<Us
   }
 }
 
-export async function signInWithProvider(ui: FirebaseUIConfiguration, provider: AuthProvider): Promise<void> {
+export async function signInWithProvider(ui: FirebaseUIConfiguration, provider: AuthProvider): Promise<never | UserCredential> {
   try {
     if (hasBehavior(ui, "autoUpgradeAnonymousProvider")) {
-      await getBehavior(ui, "autoUpgradeAnonymousProvider")(ui, provider);
-      // If we get to here, the user is not anonymous, otherwise they
-      // have been redirected to the provider's sign in page.
+      const result = await getBehavior(ui, "autoUpgradeAnonymousProvider")(ui, provider);
+     
+      // If we hit this point, the user is either not anonymous (undefined), or they have been linked
+      // via a popup flow (UserCredential). If they have been redirected, they will never get to here.
+      if (result) {
+        return result;
+      }
+      // If they hit this point, they are not anonymous and we need to sign them in.
     }
 
-    ui.setState("pending");
-
-    // TODO(ehesp): Handle popup or redirect based on behavior
-    await signInWithRedirect(ui.auth, provider);
-    // We don't modify state here since the user is redirected.
-    // If we support popups, we'd need to modify state here.
+    const strategy = getBehavior(ui, "providerSignInStrategy");
+    return await strategy(ui, provider);
   } catch (error) {
     handleFirebaseError(ui, error);
   } finally {
diff --git a/packages/core/src/behaviors.ts b/packages/core/src/behaviors.ts
index 43d0b8af..1fb0631e 100644
--- a/packages/core/src/behaviors.ts
+++ b/packages/core/src/behaviors.ts
@@ -23,6 +23,9 @@ import {
   User,
   UserCredential,
   RecaptchaVerifier,
+  signInWithRedirect,
+  signInWithPopup,
+  linkWithPopup,
 } from "firebase/auth";
 import { FirebaseUIConfiguration } from "./config";
 
@@ -32,8 +35,10 @@ export type BehaviorHandlers = {
     ui: FirebaseUIConfiguration,
     credential: AuthCredential
   ) => Promise<UserCredential | undefined>;
-  autoUpgradeAnonymousProvider: (ui: FirebaseUIConfiguration, provider: AuthProvider) => Promise<undefined | never>;
+  autoUpgradeAnonymousProvider: (ui: FirebaseUIConfiguration, provider: AuthProvider) => Promise<never | undefined | UserCredential>;
   recaptchaVerification: (ui: FirebaseUIConfiguration, element: HTMLElement) => RecaptchaVerifier;
+  providerSignInStrategy: (ui: FirebaseUIConfiguration, provider: AuthProvider) => Promise<never | UserCredential>;
+  providerLinkStrategy: (ui: FirebaseUIConfiguration, user: User, provider: AuthProvider) => Promise<never | UserCredential>;
 };
 
 export type Behavior<T extends keyof BehaviorHandlers = keyof BehaviorHandlers> = Pick<BehaviorHandlers, T>;
@@ -107,9 +112,8 @@ export function autoUpgradeAnonymousUsers(): Behavior<
       }
 
       ui.setState("pending");
-      await linkWithRedirect(currentUser, provider);
-      // We don't modify state here since the user is redirected.
-      // If we support popups, we'd need to modify state here.
+      const strategy = getBehavior(ui, "providerLinkStrategy");
+      return await strategy(ui, currentUser, provider);
     },
   };
 }
@@ -132,6 +136,33 @@ export function recaptchaVerification(options?: RecaptchaVerification): Behavior
   };
 }
 
+export function providerRedirectStrategy(): Behavior<"providerSignInStrategy" | "providerLinkStrategy"> {
+  return {
+    providerSignInStrategy: async (ui, provider) => {
+      ui.setState("pending");
+      return signInWithRedirect(ui.auth, provider);
+    },
+    providerLinkStrategy: async (ui, user, provider) => {
+      ui.setState("pending");
+      return linkWithRedirect(user, provider);
+    },
+  };
+}
+
+export function providerPopupStrategy(): Behavior<"providerSignInStrategy" | "providerLinkStrategy"> {
+  return {
+    providerSignInStrategy: async (ui, provider) => {
+      ui.setState("pending");
+      return signInWithPopup(ui.auth, provider);
+    },
+    providerLinkStrategy: async (ui, user, provider) => {
+      ui.setState("pending");
+      return linkWithPopup(user, provider);
+    },
+  };
+}
+
 export const defaultBehaviors = {
+  ...providerRedirectStrategy(),
   ...recaptchaVerification(),
 };
\ No newline at end of file