diff --git a/package-lock.json b/package-lock.json
index 3c52d83..5fd4ebe 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -28,6 +28,7 @@
         "@nestjs/testing": "^9.0.0",
         "@types/express": "^4.17.13",
         "@types/jest": "28.1.4",
+        "@types/multer": "^1.4.9",
         "@types/node": "^16.0.0",
         "@types/supertest": "^2.0.11",
         "@typescript-eslint/eslint-plugin": "^5.0.0",
@@ -2043,6 +2044,15 @@
       "integrity": "sha512-1Gjee59G25MrQGk8bsNvC6fxNiRgUlGn2wlhGf95a59DrprnnHk80FIMMFG9XHMdrfsuA119ht06QPDXA1Z7tw==",
       "dev": true
     },
+    "node_modules/@types/multer": {
+      "version": "1.4.9",
+      "resolved": "https://registry.npmjs.org/@types/multer/-/multer-1.4.9.tgz",
+      "integrity": "sha512-9NSvPJ2E8bNTc8XtJq1Cimx2Wrn2Ah48F15B2Du/hM8a8CHLhVbJMlF3ZCqhvMdht7Sa+YdP0aKP7N4fxDcrrg==",
+      "dev": true,
+      "dependencies": {
+        "@types/express": "*"
+      }
+    },
     "node_modules/@types/node": {
       "version": "16.18.60",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-16.18.60.tgz",
@@ -10311,6 +10321,15 @@
       "integrity": "sha512-1Gjee59G25MrQGk8bsNvC6fxNiRgUlGn2wlhGf95a59DrprnnHk80FIMMFG9XHMdrfsuA119ht06QPDXA1Z7tw==",
       "dev": true
     },
+    "@types/multer": {
+      "version": "1.4.9",
+      "resolved": "https://registry.npmjs.org/@types/multer/-/multer-1.4.9.tgz",
+      "integrity": "sha512-9NSvPJ2E8bNTc8XtJq1Cimx2Wrn2Ah48F15B2Du/hM8a8CHLhVbJMlF3ZCqhvMdht7Sa+YdP0aKP7N4fxDcrrg==",
+      "dev": true,
+      "requires": {
+        "@types/express": "*"
+      }
+    },
     "@types/node": {
       "version": "16.18.60",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-16.18.60.tgz",
diff --git a/package.json b/package.json
index 7b1f592..c2def4b 100644
--- a/package.json
+++ b/package.json
@@ -40,6 +40,7 @@
     "@nestjs/testing": "^9.0.0",
     "@types/express": "^4.17.13",
     "@types/jest": "28.1.4",
+    "@types/multer": "^1.4.9",
     "@types/node": "^16.0.0",
     "@types/supertest": "^2.0.11",
     "@typescript-eslint/eslint-plugin": "^5.0.0",
diff --git a/src/auth/auth.controller.ts b/src/auth/auth.controller.ts
index 47b9da9..f96019a 100644
--- a/src/auth/auth.controller.ts
+++ b/src/auth/auth.controller.ts
@@ -1,7 +1,18 @@
-import { Controller, Get, Logger, Query, Res } from '@nestjs/common';
+import {
+  Body,
+  Controller,
+  Get,
+  Logger,
+  Patch,
+  Post,
+  Query,
+  Res,
+  UseInterceptors,
+} from '@nestjs/common';
 import { Auth42Service } from './auth-42.service';
 import { AuthService } from './auth.service';
 import { UserSigninResponseDto } from './dto/user-signin-response.dto';
+import { FileInterceptor } from '@nestjs/platform-express';
 
 @Controller('auth')
 export class AuthController {
@@ -11,8 +22,8 @@ export class AuthController {
   ) {}
   private readonly logger = new Logger(AuthController.name);
 
-  @Get('/signin')
-  async signin(@Query('code') code: string, @Res() res: any) {
+  @Post('/signin')
+  async signin(@Body('code') code: string, @Res() res: any) {
     // code를 이용해 access token을 받아온다.
     const accessToken = await this.auth42Service.getAccessToken(code);
     // access token을 이용해 사용자 정보를 받아온다.
@@ -43,4 +54,13 @@ export class AuthController {
     };
     return res.send(userSigninResponseDto);
   }
+
+  // TODO: AuthGuard
+  @Patch('/login')
+  @UseInterceptors(FileInterceptor('image'))
+  async login(@Body('nickname') nickname: string) {
+    // nickname validation
+    await this.authService.validateNickname(nickname);
+    //
+  }
 }
diff --git a/src/auth/auth.service.ts b/src/auth/auth.service.ts
index 82f03a6..c61bf5f 100644
--- a/src/auth/auth.service.ts
+++ b/src/auth/auth.service.ts
@@ -1,4 +1,4 @@
-import { Injectable } from '@nestjs/common';
+import { HttpException, HttpStatus, Injectable } from '@nestjs/common';
 import { JwtService } from '@nestjs/jwt';
 import { User } from 'src/users/entities/user.entity';
 import { UserRepository } from './../users/users.repository';
@@ -33,7 +33,7 @@ export class AuthService {
   }
 
   async generateJwtToken(user: User) {
-    const payload = { id: user.id, nickname: user.nickname };
+    const payload = { id: user.id, email: user.email };
     // accessToken 생성
     const accessToken = await this.jwtService.signAsync(payload);
     // refreshToken 생성
@@ -42,4 +42,14 @@ export class AuthService {
     await this.userRepository.update(user.id, { refreshToken });
     return { jwtAccessToken: accessToken, jwtRefreshToken: refreshToken };
   }
+
+  async validateNickname(nickname: string) {
+    const user = await this.userRepository.findOneByNickname(nickname);
+    if (user) {
+      throw new HttpException(
+        '이미 존재하는 닉네임입니다.',
+        HttpStatus.CONFLICT,
+      );
+    }
+  }
 }
diff --git a/src/common/pipes/positiveInt.pipe.ts b/src/common/pipes/positiveInt.pipe.ts
new file mode 100644
index 0000000..4905dd1
--- /dev/null
+++ b/src/common/pipes/positiveInt.pipe.ts
@@ -0,0 +1,11 @@
+import { HttpException, Injectable, PipeTransform } from '@nestjs/common';
+
+@Injectable()
+export class PositiveIntPipe implements PipeTransform {
+  transform(value: number) {
+    if (value < 0) {
+      throw new HttpException('value > 0', 400);
+    }
+    return value;
+  }
+}
diff --git a/src/users/entities/user.entity.ts b/src/users/entities/user.entity.ts
index 5edca78..d7a99bc 100644
--- a/src/users/entities/user.entity.ts
+++ b/src/users/entities/user.entity.ts
@@ -12,7 +12,7 @@ import { Column, Entity, Unique } from 'typeorm';
 @Entity()
 @Unique(['nickname'])
 export class User extends BaseEntity {
-  @Column({ default: null })
+  @Column({ unique: true })
   @IsString()
   @Length(1, 10)
   @Matches(/^[ㄱ-ㅎ가-힣a-zA-Z0-9!]+$/)
diff --git a/src/users/users.repository.ts b/src/users/users.repository.ts
index 8f74368..144caef 100644
--- a/src/users/users.repository.ts
+++ b/src/users/users.repository.ts
@@ -6,4 +6,8 @@ export class UserRepository extends Repository<User> {
   constructor(@InjectRepository(User) private dataSource: DataSource) {
     super(User, dataSource.manager);
   }
+
+  async findOneByNickname(nickname: string) {
+    return await this.findOne({ where: { nickname } });
+  }
 }