Added user login & registration. Added SQL file for postgres database.

backend/nestjs-seshat-api/src/auth/strategies/login.strategy.ts

@@ -0,0 +1,20 @@
+
+import { Strategy } from 'passport-local';
+import { PassportStrategy } from '@nestjs/passport';
+import { Injectable, UnauthorizedException } from '@nestjs/common';
+import { AuthService } from '../auth.service';
+
+@Injectable()
+export class LoginStrategy extends PassportStrategy(Strategy, 'login') {
+  constructor(private authService: AuthService) {
+    super();
+  }
+
+  async validate(username: string, password: string): Promise<any> {
+    const user = await this.authService.validate(username, password);
+    if (!user) {
+      throw new UnauthorizedException();
+    }
+    return user;
+  }
+}