diff --git a/src/actions/auth/login.ts b/src/actions/auth/login.ts
index dcad3ec..5414e7a 100644
--- a/src/actions/auth/login.ts
+++ b/src/actions/auth/login.ts
@@ -246,12 +246,9 @@ async function promptAuthenticationMethod() {
       message: 'Choose authentication method:',
       choices: [
         {
-          name: chalk.dim(
-            '🔐 OAuth (Google Account) - Interactive browser authentication'
-          ),
+          name: '🔐 OAuth (Google Account) - Interactive browser authentication',
           value: 'oauth',
           short: 'OAuth',
-          disabled: chalk.dim('Work in Progress'),
         },
         {
           name: '🔑 Service Account - JSON key file authentication',
@@ -338,22 +335,20 @@ const loginAction = async (options: LoginActionType) => {
     const config = loadConfig();
     let isReauthenticate = false;
 
-    if (options.method == 'oauth') {
-      console.log(
-        chalk.gray(
-          '🔐 oauth is not implemented yet. We are working on it. Please use service-account instead.\n'
-        )
-      );
-      return;
-    }
+    // Check if already authenticated (service account or OAuth)
+    const hasServiceAccount =
+      config.serviceAccountPath && fs.existsSync(config.serviceAccountPath);
+    const hasOAuth =
+      config.authMethod === 'oauth' && fs.existsSync(CREDENTIALS_FILE);
 
-    // Check if already authenticated with service account
-    if (
-      config.serviceAccountPath &&
-      fs.existsSync(config.serviceAccountPath) &&
-      !options.force
-    ) {
-      console.log(chalk.green('✅ Already authenticated with service account'));
+    if ((hasServiceAccount || hasOAuth) && !options.force) {
+      if (hasServiceAccount) {
+        console.log(
+          chalk.green('✅ Already authenticated with service account')
+        );
+      } else {
+        console.log(chalk.green('✅ Already authenticated with OAuth'));
+      }
 
       if (config.defaultProject) {
         console.log(
@@ -380,35 +375,110 @@ const loginAction = async (options: LoginActionType) => {
 
     console.log(chalk.blue('🔐 Starting authentication process...\n'));
 
-    // Only support service account authentication
-    console.log(chalk.blue('🔑 Service Account Authentication\n'));
-    const serviceAccountPath = await promptServiceAccountFile();
+    // Determine auth method: use CLI flag or prompt the user
+    let authMethod: LoginMethod;
+    if (options.method) {
+      authMethod = options.method;
+    } else {
+      authMethod = await promptAuthenticationMethod();
+    }
 
-    const serviceAccount = JSON.parse(
-      fs.readFileSync(path.resolve(serviceAccountPath), 'utf8')
-    );
-    console.log(chalk.green('✅ Service account loaded successfully!'));
-    console.log(chalk.gray(`   └── Project: ${serviceAccount.project_id}`));
-
-    // Save service account info to config for future use
-    const newConfig = {
-      ...config,
-      serviceAccountPath: path.resolve(serviceAccountPath),
-      defaultProject: serviceAccount.project_id,
-    };
-
-    saveConfig(newConfig);
-    console.log(chalk.green(`✅ Service account saved for future use`));
-    console.log(
-      chalk.green(`✅ Default project set to: ${serviceAccount.project_id}`)
-    );
+    if (authMethod === 'oauth') {
+      const credentials = await authenticateWithOAuth();
 
-    console.log(
-      chalk.green('\n🎉 Setup complete! You can now use all commands.')
-    );
-    console.log(
-      chalk.gray('💡 No need to specify --service-account flag anymore')
-    );
+      console.log(chalk.green('\n✅ OAuth authentication successful!'));
+      console.log(chalk.gray('   └── Access token received'));
+
+      // Try to fetch available Firebase projects and let the user pick one
+      let defaultProject: string | undefined;
+      try {
+        const { listUserProjects } = await import('@/actions/auth/projects');
+        const projects = await listUserProjects(credentials);
+
+        if (projects.length > 0) {
+          const projectChoices = projects.map((p) => ({
+            name: `${p.name} (${p.projectId})`,
+            value: p.projectId,
+            short: p.projectId,
+          }));
+
+          const { selectedProject } = await inquirer.prompt([
+            {
+              type: 'list',
+              name: 'selectedProject',
+              message: 'Select a default Firebase project:',
+              choices: projectChoices,
+            },
+          ]);
+
+          defaultProject = selectedProject;
+        } else {
+          console.log(
+            chalk.yellow(
+              '⚠️  No Firebase projects found for your account. You can set one later with: firebase-tools-cli projects --set-default <projectId>'
+            )
+          );
+        }
+      } catch (projectError) {
+        console.log(
+          chalk.yellow(
+            '⚠️  Could not fetch projects automatically. You can set a default project later with: firebase-tools-cli projects --set-default <projectId>'
+          )
+        );
+      }
+
+      // Save OAuth credentials and remove service account from config
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      const { serviceAccountPath: _removed, ...restConfig } = config;
+      const newConfig = {
+        ...restConfig,
+        authMethod: 'oauth' as const,
+        ...(defaultProject ? { defaultProject } : {}),
+      };
+
+      saveConfig(newConfig);
+
+      console.log(chalk.green('\n✅ OAuth credentials saved for future use'));
+      if (defaultProject) {
+        console.log(
+          chalk.green(`✅ Default project set to: ${defaultProject}`)
+        );
+      }
+      console.log(
+        chalk.green('\n🎉 Setup complete! You can now use all commands.')
+      );
+    } else {
+      // Service account authentication
+      console.log(chalk.blue('🔑 Service Account Authentication\n'));
+      const serviceAccountPath = await promptServiceAccountFile();
+
+      const serviceAccount = JSON.parse(
+        fs.readFileSync(path.resolve(serviceAccountPath), 'utf8')
+      );
+      console.log(chalk.green('✅ Service account loaded successfully!'));
+      console.log(chalk.gray(`   └── Project: ${serviceAccount.project_id}`));
+
+      // Save service account info to config for future use
+      const newConfig = {
+        ...config,
+        authMethod: 'service-account' as const,
+        serviceAccountPath: path.resolve(serviceAccountPath),
+        defaultProject: serviceAccount.project_id,
+      };
+
+      saveConfig(newConfig);
+      console.log(chalk.green(`✅ Service account saved for future use`));
+      console.log(
+        chalk.green(`✅ Default project set to: ${serviceAccount.project_id}`)
+      );
+
+      console.log(
+        chalk.green('\n🎉 Setup complete! You can now use all commands.')
+      );
+      console.log(
+        chalk.gray('💡 No need to specify --service-account flag anymore')
+      );
+    }
   } catch (error) {
     const errorMessage = error instanceof Error ? error.message : String(error);
 
diff --git a/src/actions/auth/projects.ts b/src/actions/auth/projects.ts
index 8be27a3..ab289dd 100644
--- a/src/actions/auth/projects.ts
+++ b/src/actions/auth/projects.ts
@@ -4,6 +4,7 @@ import fs from 'fs';
 import { Credentials, OAuth2Client } from 'google-auth-library';
 import path from 'path';
 
+import { CREDENTIALS_FILE } from '@/constants';
 import { loadConfig, saveConfig } from '@/utils';
 
 type ProjectType = {
@@ -215,6 +216,59 @@ const listProjectsAction = async (
       }
     }
 
+    // Check for saved OAuth credentials
+    if (config.authMethod === 'oauth' && fs.existsSync(CREDENTIALS_FILE)) {
+      let savedCredentials: Credentials;
+      try {
+        savedCredentials = JSON.parse(
+          fs.readFileSync(CREDENTIALS_FILE, 'utf8')
+        );
+      } catch {
+        console.error(chalk.red('❌ Saved OAuth credentials are corrupted'));
+        console.log(chalk.yellow('💡 Try: firebase-tools-cli login --force'));
+        return;
+      }
+
+      console.log(chalk.blue('🔐 Using saved OAuth authentication'));
+
+      const projects = await listUserProjects(savedCredentials);
+
+      if (projects.length > 0) {
+        console.log(chalk.cyan('\nYour Firebase Projects:\n'));
+        projects.forEach((project) => {
+          const isDefault = project.projectId === config.defaultProject;
+          const marker = isDefault ? chalk.green(' ✓ (default)') : '';
+          console.log(
+            chalk.white(`📁 ${project.name || project.projectId}`) + marker
+          );
+          console.log(chalk.gray(`   └── ID: ${project.projectId}`));
+          console.log(chalk.gray(`   └── Type: OAuth`));
+          console.log();
+        });
+      } else {
+        if (config.defaultProject) {
+          console.log(chalk.cyan('Default Project:\n'));
+          console.log(chalk.white(`📁 ${config.defaultProject}`));
+          console.log(chalk.gray(`   └── ID: ${config.defaultProject}`));
+          console.log(chalk.gray(`   └── Type: OAuth`));
+          console.log(chalk.green(`   └── Status: ✓ (default)`));
+        } else {
+          console.log(chalk.yellow('⚠️  No projects found for your account'));
+        }
+      }
+
+      console.log();
+      console.log(chalk.blue('💡 Commands:'));
+      console.log(
+        chalk.gray('   • firebase-tools-cli projects --set-default <projectId>')
+      );
+      console.log(
+        chalk.gray('   • firebase-tools-cli projects --clear-default')
+      );
+      console.log(chalk.gray('   • firebase-tools-cli reset --config-only'));
+      return;
+    }
+
     console.log(chalk.yellow('🔐 No authentication found'));
     console.log(chalk.gray('Run: firebase-tools-cli login'));
     console.log(
diff --git a/src/hooks/init.ts b/src/hooks/init.ts
index d0d65bc..91af613 100644
--- a/src/hooks/init.ts
+++ b/src/hooks/init.ts
@@ -2,9 +2,11 @@ import chalk from 'chalk';
 import { Command } from 'commander';
 import * as admin from 'firebase-admin';
 import fs from 'fs';
+import { Credentials, OAuth2Client } from 'google-auth-library';
 import inquirer from 'inquirer';
 import path from 'path';
 
+import { CREDENTIALS_FILE, OAUTH_CONFIG } from '@/constants';
 import { loadConfig, saveConfig } from '@/utils';
 
 async function promptServiceAccountFile() {
@@ -103,6 +105,42 @@ async function configureAdminServiceAccount(
   return { db, credential, projectId };
 }
 
+async function configureAdminOAuth(
+  credentials: Credentials,
+  projectId: string
+) {
+  const oauth2Client = new OAuth2Client(
+    OAUTH_CONFIG.clientId,
+    OAUTH_CONFIG.clientSecret,
+    OAUTH_CONFIG.redirectUri
+  );
+  oauth2Client.setCredentials(credentials);
+
+  const credential: admin.credential.Credential = {
+    getAccessToken: async () => {
+      const tokenResponse = await oauth2Client.getAccessToken();
+      if (!tokenResponse.token) {
+        throw new Error('Failed to retrieve OAuth access token');
+      }
+      const expiresIn =
+        (tokenResponse.res?.data as { expires_in?: number } | undefined)
+          ?.expires_in ?? 3600;
+      return {
+        access_token: tokenResponse.token,
+        expires_in: expiresIn,
+      };
+    },
+  };
+
+  console.log(chalk.blue(`🔐 Using OAuth authentication`));
+  console.log(chalk.gray(`   └── Project: ${projectId}`));
+
+  admin.initializeApp({ credential, projectId });
+  const db = admin.firestore();
+
+  return { db, credential, projectId };
+}
+
 async function initializeFirebase(thisCommand: Command) {
   const commandName = thisCommand.args[0];
   const skipAuthCommands = ['reset', 'logout', 'login', 'docs', 'convert'];
@@ -153,6 +191,35 @@ async function initializeFirebase(thisCommand: Command) {
         return;
       }
 
+      // Check for saved OAuth credentials
+      if (config.authMethod === 'oauth' && fs.existsSync(CREDENTIALS_FILE)) {
+        let savedCredentials: Credentials;
+        try {
+          savedCredentials = JSON.parse(
+            fs.readFileSync(CREDENTIALS_FILE, 'utf8')
+          );
+        } catch {
+          throw new Error(
+            'Saved OAuth credentials are corrupted. Please run: firebase-tools-cli login --force'
+          );
+        }
+
+        projectIdValue = projectIdValue || config.defaultProject;
+
+        if (!projectIdValue) {
+          console.log(chalk.yellow('⚠️  No default project configured'));
+          console.log(
+            chalk.gray(
+              '   Run: firebase-tools-cli projects --set-default <projectId>'
+            )
+          );
+          process.exit(1);
+        }
+
+        await configureAdminOAuth(savedCredentials, projectIdValue);
+        return;
+      }
+
       console.log(chalk.yellow('🔐 No authentication found'));
       console.log(
         chalk.blue("Let's set up service account authentication...\n")
diff --git a/src/utils.ts b/src/utils.ts
index 2a62aee..6885654 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -6,8 +6,9 @@ import inquirer from 'inquirer';
 import { CONFIG_DIR, CONFIG_FILE, CREDENTIALS_FILE } from './constants';
 
 type ConfigType = {
-  authMethod: string;
+  authMethod?: 'oauth' | 'service-account';
   serviceAccountPath?: string;
+  defaultProject?: string;
 };
 
 function countNodes(data: any, count: number = 0): number {