CORS configuration in Security in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable CORS in a Spring Security configuration.

Spring Boot

http.cors([1]());

Drag options to blanks, or click blank then click option'

AwithDefaults()

Band

Cdisable

Dconfigure

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'disable' disables CORS.

Using 'and' or 'configure' are not valid here.

The cors(withDefaults()) method enables CORS support in Spring Security. Calling withDefaults() activates it with default settings.

2fill in blank

medium

Complete the code to define a CORS configuration source bean.

Spring Boot

@Bean
public CorsConfigurationSource [1]() {
    CorsConfiguration configuration = new CorsConfiguration();
    configuration.addAllowedOrigin("*");
    UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
    source.registerCorsConfiguration("/**", configuration);
    return source;
}

Drag options to blanks, or click blank then click option'

AcorsSource

BcorsSetup

CcorsConfig

DcorsConfigurationSource

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that Spring Security does not recognize will cause CORS to not be applied.

Using generic names like 'corsSetup' may not be detected automatically.

The method name corsConfigurationSource is the standard name Spring Security looks for to get CORS settings.

3fill in blank

hard

Fix the error in the CORS configuration to allow credentials.

Spring Boot

CorsConfiguration configuration = new CorsConfiguration();
configuration.setAllowCredentials([1]);

Drag options to blanks, or click blank then click option'

Afalse

Btrue

Cnull

D"true"

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a string like "true" instead of the Boolean true causes errors.

Passing null disables the setting.

The setAllowCredentials method expects a Boolean true or false, not a string or null.

4fill in blank

hard

Fill both blanks to restrict allowed HTTP methods to GET and POST in CORS configuration.

Spring Boot

CorsConfiguration configuration = new CorsConfiguration();
configuration.setAllowedMethods(List.of([1], [2]));

Drag options to blanks, or click blank then click option'

A"GET"

B"POST"

C"PUT"

D"DELETE"

Attempts:

3 left

💡 Hint

Common Mistakes

Including methods like PUT or DELETE when only GET and POST are desired.

Passing method names without quotes causes syntax errors.

To allow only GET and POST methods, pass their names as strings in the allowed methods list.

5fill in blank

hard

Fill all three blanks to create a complete Spring Security CORS configuration bean with allowed origins, methods, and credentials.

Spring Boot

CorsConfiguration configuration = new CorsConfiguration();
configuration.setAllowedOrigins(List.of([1]));
configuration.setAllowedMethods(List.of([2]));
configuration.setAllowCredentials([3]);

Drag options to blanks, or click blank then click option'

A"https://example.com"

B"GET"

Ctrue

D"*"

Attempts:

3 left

💡 Hint

Common Mistakes

Using "*" for allowed origins disables credentials support.

Passing strings instead of Boolean for allowCredentials causes errors.

This sets allowed origins to a specific URL, allowed methods to GET, and enables credentials support.

Practice

1. What is the main purpose of configuring CORS in a Spring Boot security setup?

easy

A. To control which external websites can access your backend resources

B. To improve database query performance

C. To manage user authentication tokens

D. To style the frontend user interface

Solution

1. Step 1: Understand CORS role in web security

   CORS (Cross-Origin Resource Sharing) controls which external domains can call your backend APIs.

2. Step 2: Identify the purpose in Spring Boot security

   Configuring CORS in Spring Security allows safe cross-site requests by specifying allowed origins and methods.

3. Final Answer:

   To control which external websites can access your backend resources -> Option A

4. Quick Check:

   CORS controls access origins = A [OK]

Hint: CORS = Cross-Origin access control [OK]

Common Mistakes:

• Confusing CORS with authentication
• Thinking CORS improves database speed
• Assuming CORS styles frontend

2. Which of the following is the correct way to enable CORS in a Spring Security configuration class?

easy

A. http.corsEnabled(true);

B. http.enableCors();

C. http.allowCors(true);

D. http.cors().and().csrf().disable();

Solution

1. Step 1: Recall Spring Security CORS enabling syntax

   Spring Security uses the method http.cors() to enable CORS support.

2. Step 2: Identify the correct chaining method

   The correct chaining to disable CSRF and enable CORS is http.cors().and().csrf().disable();

3. Final Answer:

   http.cors().and().csrf().disable(); -> Option D

4. Quick Check:

   Enable CORS with http.cors() = C [OK]

Hint: Use http.cors() to enable CORS in Spring Security [OK]

Common Mistakes:

• Using non-existent methods like enableCors()
• Forgetting to chain with .and()
• Confusing CORS enabling with CSRF

3. Given this Spring Security CORS configuration snippet, what origins are allowed?

@Bean
public CorsConfigurationSource corsConfigurationSource() {
  CorsConfiguration configuration = new CorsConfiguration();
  configuration.setAllowedOrigins(List.of("https://example.com", "https://app.example.com"));
  configuration.setAllowedMethods(List.of("GET", "POST"));
  UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
  source.registerCorsConfiguration("/**", configuration);
  return source;
}

medium

A. No origins are allowed because configuration is incomplete

B. Requests from any origin are allowed

C. Only requests from https://example.com and https://app.example.com are allowed

D. Only GET requests from any origin are allowed

Solution

1. Step 1: Analyze allowed origins list

   The code sets allowed origins explicitly to "https://example.com" and "https://app.example.com".

2. Step 2: Understand effect on requests

   Only requests coming from these two origins will be accepted; others will be blocked by CORS policy.

3. Final Answer:

   Only requests from https://example.com and https://app.example.com are allowed -> Option C

4. Quick Check:

   Allowed origins = example.com and app.example.com = D [OK]

Hint: Allowed origins list controls which sites can call backend [OK]

Common Mistakes:

• Assuming all origins allowed by default
• Confusing allowed methods with allowed origins
• Thinking configuration is incomplete without headers

4. Identify the error in this Spring Security CORS configuration code:

@Bean
public CorsConfigurationSource corsConfigurationSource() {
  CorsConfiguration configuration = new CorsConfiguration();
  configuration.setAllowedOrigins("*");
  configuration.setAllowedMethods(List.of("GET", "POST"));
  UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
  source.registerCorsConfiguration("/**", configuration);
  return source;
}

medium

A. Allowed methods list is missing PUT and DELETE

B. setAllowedOrigins expects a list, not a single string

C. UrlBasedCorsConfigurationSource cannot be used here

D. The method should return void, not CorsConfigurationSource

Solution

1. Step 1: Check setAllowedOrigins parameter type

   The method setAllowedOrigins requires a List<String>, but the code passes a single String "*".

2. Step 2: Understand correct usage for wildcard

   To allow all origins, use List.of("*") instead of a plain string.

3. Final Answer:

   setAllowedOrigins expects a list, not a single string -> Option B

4. Quick Check:

   Allowed origins must be List<String> = B [OK]

Hint: setAllowedOrigins needs a list, not a string [OK]

Common Mistakes:

• Passing a string instead of a list to setAllowedOrigins
• Ignoring method parameter types
• Assuming missing HTTP methods cause errors here

5. You want to allow all origins but only GET and POST methods in your Spring Security CORS config. Which code snippet correctly achieves this while following best practices?

hard

A. configuration.setAllowedOriginPatterns(List.of("*")); configuration.setAllowedMethods(List.of("GET", "POST"));

B. configuration.setAllowedOrigins(List.of("*")); configuration.setAllowedMethods(List.of("GET", "POST"));

C. configuration.setAllowedOrigins("*"); configuration.setAllowedMethods(List.of("GET", "POST"));

D. configuration.setAllowedOrigins(List.of("*")); configuration.setAllowedMethods(List.of("GET", "POST", "PUT"));

Solution

1. Step 1: Understand wildcard origin allowance

   Using setAllowedOrigins(List.of("*")) is deprecated and may cause issues; instead, setAllowedOriginPatterns supports wildcards properly.

2. Step 2: Check allowed methods correctness

   Only GET and POST methods are allowed as required.

3. Final Answer:

   configuration.setAllowedOriginPatterns(List.of("*")); configuration.setAllowedMethods(List.of("GET", "POST")); -> Option A

4. Quick Check:

   Use allowedOriginPatterns for wildcard origins = A [OK]

Hint: Use setAllowedOriginPatterns for wildcard origins [OK]

Common Mistakes:

• Using setAllowedOrigins with "*" string
• Allowing extra HTTP methods by mistake
• Passing string instead of list to allowed origins