Note: This is our master guide on API Security where we solve common developer queries in detail with how-to guides, common examples and code snippets. Feel free to visit the smaller guides linked later in this article on topics such as authentication methods, rate limiting, API monitoring and more.
Today, an average SaaS company relies on 350 integrations to share data and functionality, both internally andwith the tools their customers already use. That reliance makes API security afoundational requirement, not an afterthought — a single overlookedvulnerability can expose sensitive data, compromise user privacy, and disruptoperations for every customer connected through that API.
This guide is Knit's masterreference on API security. In it, you'll find:
• The most common API security risks and how they happen
• Eight best practices for securing your APIs, withpractical, step-by-step guidance
• How these practices map to the OWASP API Security Top 10, the industry-standard framework for API vulnerabilities
• An on-page API security checklist you can work throughdirectly (plus a downloadable version)
• Answers to the API security questions developers askmost
Whether you're securing the APIsyou build or evaluating the third-party APIs you integrate with, thesepractices apply either way. Let's get started.
TABLE OF CONTENTS
• API Security Risks
• API security best practices
1. API Authentication and Authorization methods
2. Secure data transmission: Encryption and HTTPS
3. Input validation and parameter sanitization
4. Rate limiting and Throttling
5. API monitoring and logging
6. Regular security audits and Penetration Testing
7. API lifecycle management and decommissioning
8. Third-Party API Security Considerations
• OWASP API Security Top 10: How These Practices Map
• API security checklist
• Common API security FAQs by developers
• Enable maximum security for your API integrations withKnit
API Security Risks
Before diving deeper into the API security best practices, it's crucial to have a solid grasp of the risks and threats that APIs can face. These risks can stem from various sources, both external and internal, and being aware of them is the first step towards effective protection.
Here are some of the key API security risks to consider:
- Unauthorized access
- Broken authentication tokens
- Injection attacks
- Data exposure
- Rate limiting and Denial of Service (DoS) attacks
- Third party dependencies
- Human error
Read: Common Risks to API Security and their consequences where we discussed all these threats in detail
The old adage "prevention is better than cure" couldn't be more apt in the realm of API security, where a proactive approach is the key to averting devastating consequences for all parties involved.
Keeping this in mind, let’s dive deeper into our API security best practices.
API security best practices
Ensuring API security means providing a safe way for authentication, authorization, data transfer and more.
1. API Authentication and Authorization methods
API authentication and authorization methods are the most essential components of modern web and software development. These methods play a crucial role in ensuring the security and integrity of the data exchanged between systems and applications.
Authentication verifies the identity of users or systems accessing an API, while authorization determines what actions or resources they are allowed to access.
With a variety of techniques and protocols available, such as API keys, OAuth, and token-based systems, developers have the flexibility to choose the most suitable approach to protect their APIs and the data they manage.
Read our article on API Authentication Best Practices where we discuss top 5 authentication protocols such as OAuth, Bearer tokens, Basic auth, JWT and API keys in detail.
While choosing the right protocol depends on your specific use case and security requirements, here's a quick comparison of the 5 API authentication methods:
Now, let’s explore how data can be transferred securely between API calls.
2. Secure data transmission: Encryption and HTTPS
When it comes to API security, ensuring that data is transmitted securely is an absolute must.
Imagine your data is like a confidential letter traveling from sender to receiver through the postal service. Just as you'd want that letter to be sealed in an envelope to prevent prying eyes from seeing its contents, data encryption in transit ensures that the information exchanged between clients and servers is kept safe and confidential during its journey across the internet.
HTTPS
The go-to method for achieving this security is HTTPS, which is like the secure postal service for your data.
HTTPS uses Transport Layer Security (TLS) or its predecessor, Secure Sockets Layer (SSL), to encrypt data before it leaves the sender's location and decrypt it only when it reaches the intended recipient.
Think of TLS/SSL certificates as the unique stamps on your sealed letter; they ensure that the data's journey is tamper-proof and that it's delivered only to the right address.
So, whenever you see that little padlock icon in your browser's address bar, rest assured that your data is traveling securely, just like that confidential letter in its sealed envelope.
In a world where data breaches are a constant threat, secure data transmission is like the lock and key that keeps your digital communication safe from potential eavesdroppers.
Note: As an API aggregator, Knit, prioritizes user privacy and commit to keeping your data safe in the best way possible. All data at Knit is doubly encrypted at rest with AES 256 bit encryption and in transit with TLS 1.3. Plus, all PII and user credentials are encrypted with an additional layer of application security. Learn more about Knit's security practices here
3. Input validation and parameter sanitization
In the world of API security, one area that often flies under the radar but is absolutely critical is input validation and parameter sanitization. It's like inspecting every ingredient that goes into a recipe; if you miss something harmful, the entire dish could turn out toxic.
First, let's talk about the risks.
Input validation failures can open the door to a variety of malicious attacks, with one of the most notorious being injection attacks.
These crafty attacks involve malicious code or data being injected into an API's input fields, exploiting vulnerabilities and wreaking havoc. Two common types are SQL injection and Cross-Site Scripting (XSS), both of which can lead to data breaches and system compromise.
To learn more about injection vulnerabilities, read Common API Security Threats Developers Must Know About
How to defend against injection attacks
Well, think of sanitizing user inputs as thoroughly washing your hands before handling food – it's a fundamental hygiene practice.
By rigorously examining and cleaning incoming data, we can block malicious code from getting through. For instance, when dealing with user-generated content, we should sanitize inputs to remove potentially harmful scripts or queries.
Additionally, for database queries, you should use parameterized statements instead of injecting user inputs directly into SQL queries. This way, even if an attacker tries a SQL injection, their input gets treated as data rather than executable code.
In the above example, we use a parameterized statement (? as a placeholder) to safely handle user input, preventing SQL injection by treating the input as data rather than executable SQL code.
In essence, input validation and parameter sanitization are like the gatekeepers of your API, filtering out the bad actors and ensuring the safety of your system. It's not just good practice; it's a crucial line of defense in the world of API security.
4. Rate limiting and Throttling
Both rate limiting and throttling are critical components of API security, as they help maintain the availability and performance of API services, protect them against abusive usage, and ensure a fair distribution of resources among clients.
Rate limiting restricts the number of API requests a client can make within a specific timeframe (e.g. requests per second or minute) while throttling is a more flexible approach that slows down or delays the processing of requests from clients who exceeded their allotted rate limit instead of denying requests outright.
Throttling is useful for ensuring a more graceful degradation of service and a smoother user experience when rate limits are exceeded. The exhaustion of rate limits are often denoted by HTTP error code 429.
These techniques are often implemented in combination with each other to create a comprehensive defense strategy for APIs.
Read: 10 API rate limiting best practices to deal with HTTP error code 429
5. API monitoring and logging
API monitoring and logging are vital for proactive security measures, threat detection, and incident response.
API monitoring involves the continuous observation of API traffic and activities in real-time. It allows for immediate detection of unusual or suspicious behavior, such as spikes in traffic or unexpected access patterns. Beyond security, it also aids in optimizing performance by identifying bottlenecks, latency issues, or errors in API responses, ensuring smooth and efficient operation.
API logging involves the recording of all API interactions and events over time. This creates a detailed historical record that can be invaluable for forensic analysis, compliance, and auditing. They are invaluable for debugging and troubleshooting, as they contain detailed information about API requests, responses, errors, and performance metrics.
Monitoring and logging systems can also trigger alerts or notifications when predefined security thresholds are breached, enabling rapid incident response.
Access Logs and Issues in one page
This is exactly what Knit does.Alongside giving you access to 100+ HRIS, ATS, CRM, and other SaaS platformsthrough a single unified API, Knit also takes care of API logging andmonitoring for every connected integration.
Knit's Logs and Issues pagegives you a one-page historical overview of all your webhooks and integratedaccounts, including a count of API calls and filters to narrow down by platform, account, or time range. This helps you stay on top of integration healthwithout building separate logging for each platform you support.
For a deeper look at what tolog, where logs are stored, and the tools teams commonly use, see Knit's guideto API Monitoring and Logging.
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6. Regular security audits and Penetration Testing
Regular security audits and penetration testing are critical components of a comprehensive API security strategy. They help identify vulnerabilities, assess the effectiveness of existing security measures, and ensure that an API remains resilient to evolving threats.
- Security audits involve a thorough review of an API's design, architecture, and implementation to identify security weaknesses, misconfigurations, and best practice violations, and assess whether an API adheres to security policies, standards, and regulatory requirements. This is also important for ensuring compliance with data protection laws and industry regulations.
- Meanwhile Penetration testing, or pen testing, involves simulating cyberattacks to identify vulnerabilities, weaknesses, and potential entry points that malicious actors could exploit. It attempt to exploit API vulnerabilities in a controlled environment to assess the API's resilience against real-world threats, including SQL injection, cross-site scripting (XSS), and more.
The results of penetration testing provide insights into the API's security posture, allowing organizations to prioritize and remediate high-risk vulnerabilities. Penetration tests should be conducted regularly, especially when changes or updates are made to the API, to ensure that security measures remain effective over time.
These practices are essential for safeguarding sensitive data and ensuring the trustworthiness of API-based services.
7. API lifecycle management and decommissioning
A comprehensive approach to API security involves not only establishing APIs securely but also systematically retiring and decommissioning them when they are no longer needed or viable.
This process involves clearly documenting the API's purpose, usage, and dependencies from the outset to facilitate informed decisions during the decommissioning phase. Also, you should implement version control and deprecation policies, enabling a gradual transition for API consumers and regularly audit and monitor API usage and access controls to detect potential security risks.
When decommissioning an API, the sunset plan should be communicated with stakeholders while providing ample notice, and assistance to the users in migrating to alternative APIs or solutions.
Finally, a thorough security assessment and testing should be conducted before decommissioning to identify and resolve any vulnerabilities, to ensure that the process is executed securely and without compromising data or system integrity.
Read: Developer's guide to API lifecycle management
8. Third-Party API Security Considerations
When integrating third-party APIs into your application, it's crucial to consider several important security factors.
- First and foremost, thoroughly review the reputation and trustworthiness of the API provider. Assess their security practices and history of vulnerabilities.
- Additionally, scrutinize the permissions and access levels you grant to the third-party API. Only provide the minimum access necessary for your application to function to limit potential risks.
- Monitor the API's security updates and patch management, as vulnerabilities may emerge over time.
- Ensure that data transmitted between your application and the third-party API is encrypted and protected to safeguard against interception or tampering.
- Lastly, have contingency plans in place for potential downtime or security breaches in the third-party API, which might affect your application's availability and data security.
These five checks — providerreputation, minimum necessary permissions, ongoing patch monitoring, encrypteddata in transit, and a contingency plan — are also the basis for the‘Third-party API review’ items in the checklist below.
8. OWASP API Security Top 10: How These Practices Map
The OWASP API Security Top 10(2023) is the industry-standard framework for the most critical APIvulnerability categories, maintained by the Open Web Application SecurityProject. It's worth keeping on hand alongside the best practices above — here'show each category maps to the sections in this guide:
• API1: Broken Object Level Authorization — occurs whenan API lets a user access or modify another user's data by changing an ID in arequest. Addressed by Section 1 (Authentication and Authorization methods),which covers verifying not just who a user is but what specific resourcesthey're allowed to touch.
• API2: Broken Authentication — weak or missing checks ontokens, passwords, and API keys that let attackers compromise accounts.Addressed by Section 1.
• API3: Broken Object Property Level Authorization — anAPI exposes or allows changes to data fields a client shouldn't see or edit,even if overall access is authorized. Addressed by Sections 1 and 3 (Inputvalidation and parameter sanitization), which limit what fields a request canread or write.
• API4: Unrestricted Resource Consumption — an API withno limits on request frequency, payload size, or processing cost, opening thedoor to denial-of-service issues and runaway costs. Addressed directly bySection 4 (Rate limiting and Throttling).
• API5: Broken Function Level Authorization —access-control gaps that let regular users reach administrative or privilegedendpoints. Addressed by Section 1.
• API6: Unrestricted Access to Sensitive Business Flows —an API exposes a multi-step business process (like checkout or accountcreation) without checks on whether a request is following the intended flow.Addressed by Section 6 (Regular security audits and Penetration Testing), wherethis kind of abuse is most reliably caught.
• API7: Server-Side Request Forgery (SSRF) — an APIaccepts a user-supplied URL and fetches it without validating the destination,letting an attacker reach internal systems. Addressed by Sections 2 and 3,which cover validating and sanitizing everything an API sends or receives.
• API8: Security Misconfiguration — open storage, verboseerror messages, missing security headers, or overly permissive CORS settings.Addressed by Section 2 (Encryption and HTTPS) and Section 6 (audits).
• API9: Improper Inventory Management — undocumented,deprecated, or debug API versions left exposed. Addressed directly by Section 7(API lifecycle management and decommissioning).
• API10: Unsafe Consumption of APIs — trusting data froma third-party API without validating it, so a compromised upstream APIcompromises you too. Addressed directly by Section 8 (Third-Party API SecurityConsiderations).
For the full detail behind eachcategory, including real-world examples, the OWASP API Security Projectmaintains the authoritative reference at owasp.org. Use the list above as aquick cross-check against the best practices in this guide — if a section abovefeels thin for your use case, the corresponding OWASP category is a good placeto dig deeper.
API security checklist
Use this checklist as a workingreference when building, reviewing, or integrating with APIs. It follows thesame structure as the best practices above — and maps to the OWASP API SecurityTop 10 categories covered in the previous section.
Authentication and authorization
• Use a standard protocol (OAuth 2.0, API keys, or JWTs)appropriate to your use case
• Issue short-lived access tokens with refresh tokensrather than long-lived credentials
• Scope tokens and API keys to the minimum permissionsneeded
• Check authorization on every request, not just at login
Encryption and transport security
• Enforce HTTPS (TLS 1.2+) on every endpoint — noplaintext HTTP
• Encrypt sensitive data at rest, in addition to intransit
• Set security headers and restrict CORS to known origins
Input validation and sanitization
• Validate and sanitize every input field, includingheaders and query parameters
• Use parameterized queries for all database access —never concatenate user input into SQL
• Restrict which object fields a request can read orwrite (avoid mass-assignment issues)
Rate limiting and throttling
• Set per-client rate limits based on API key, token, orIP
• Return HTTP 429 with a Retry-After header when limitsare exceeded
• Tier limits by endpoint cost and client type
Monitoring and logging
• Log every request and response, including timestamps,status codes, and caller identity
• Set alerts for unusual traffic patterns or spikes inerrors
• Retain logs long enough to support debugging, audits,and incident response
Lifecycle management
• Document each API version's purpose, usage, anddependencies
• Apply version control and deprecation policies withadvance notice to consumers
• Conduct a security review before decommissioning anyAPI
Third-party API review
• Vet the security track record and reputation of anythird-party API provider
• Grant only the minimum access scopes the integrationneeds
• Monitor third-party APIs for security updates andbreaking changes
• Have a contingency plan for third-party API downtime ora security incident upstream
To download checklist, click here
Common API security FAQs by developers
What is the OWASP API Security Top 10?
The OWASP API Security Top 10 is the industry-standard list of the most critical security risks specific to APIs, maintained by the Open Web Application Security Project and most recently updated in 2023. It covers risks such as Broken Object Level Authorization, Broken Authentication, Unrestricted Resource Consumption, Server-Side RequestForgery, and Unsafe Consumption of APIs, among others. Unlike the general OWASP Top 10, which focuses on web application vulnerabilities broadly, this list addresses issues unique to how APIs expose data and business logic throughendpoints. The best practices in this guide map directly to each of these tencategories — see the OWASP API Security Top 10 section above for the full mapping. Reviewing your APIs against this list is one of the most efficientways to prioritize security work.
What are the most common API security risks?
The most common API security risks include unauthorized access from weak or broken authentication, injection attacks such as SQL injection and cross-site scripting, excessive data exposure through endpoints that return more information than needed, lack of rate limiting that leaves APIs open to abuse, and security misconfigurations such as missing headers or overly verbose error messages. Third-party dependencies and human error round out the list — a vulnerability in an API you integrate with, or a single misconfigured permission, can compromise your application even if your own code is otherwise secure. This guide's section on API security risks covers each of these in more depth. Addressing them systematically, using the OWASP API Security Top 10 as a checklist, is the most reliable way to reduce your API's attack surface.
What should be on an API security checklist?
A solid API security checklistcovers six areas: authentication and authorization (strong protocols,short-lived tokens, least-privilege scopes), encryption (HTTPS/TLS for alltraffic and encryption at rest), input validation (sanitizing every parameter andusing parameterized queries), rate limiting (per-client limits with HTTP 429responses), monitoring and logging (recording every request, response, anderror), and third-party API review (vetting providers and limiting the accessyou grant them). The full checklist earlier in this guide breaks each area intospecific, actionable items. Knit handles several of these — encryption,logging, and monitoring — automatically for every one of the 100+ platforms itconnects, which is useful if your checklist spans many integrations rather thana single API.
What's the difference between the OWASP Top 10 and the OWASP API SecurityTop 10?
The OWASP Top 10 is a broad listof the most critical risks to web applications generally, covering issues like injection, broken access control, and security misconfiguration across any type of application. The OWASP API Security Top 10 is a separate, API-specific listthat focuses on risks unique to how APIs expose data and functionality through endpoints — such as Broken Object Level Authorization, where an API lets a user access another user's data by changing an ID in a request, or Unrestricted ResourceConsumption, where an API has no limits on request volume or payload size. If you're building or securing APIs specifically, the API Security Top 10 is the more directly applicable framework, though both lists are maintained by OWASP and complement each other.
What are API authentication best practices?
Strong API authentication startswith choosing the right protocol for the job — OAuth 2.0 for delegated access,API keys for simple server-to-server calls, or JWTs for stateless sessionvalidation — and applying it consistently. From there, best practices includeissuing short-lived access tokens with refresh tokens rather than long-livedcredentials, scoping tokens to the minimum permissions needed, and rotating APIkeys regularly. Authorization should be checked on every request, not just atlogin, to avoid the broken object- and function-level access issues covered inthe OWASP mapping above. For teams managing authentication across manythird-party APIs rather than just their own, Knit handles OAuth flows, tokenrefresh, and credential storage for every connected platform, removing a commonsource of authentication-related security gaps.
What are rate limiting best practices for REST APIs?
Effective rate limiting startswith setting per-client limits based on an API key, token, or IP address, andreturning an HTTP 429 (Too Many Requests) response with a Retry-After headerwhen a client exceeds them. Many APIs combine hard limits with throttling —slowing requests down rather than rejecting them outright — so the servicedegrades gracefully under load instead of failing. Limits should be tiered byendpoint cost and client type, and logging rate-limit events helps identifyclients that need higher limits or are misbehaving. Knit's guide to API ratelimiting and throttling covers these patterns in more detail, including how tohandle 429 responses when integrating with third-party APIs that enforce theirown limits.
How does Knit keep API integrations secure?
Knit secures every integrationwith AES-256 encryption at rest and TLS 1.3 in transit, with an additionallayer of encryption for PII and user credentials. Beyond encryption, Knit isSOC2, GDPR, and ISO27001 certified, and its infrastructure is continuouslymonitored with intrusion detection systems backed by a 24/7 support team. Forteams evaluating third-party APIs as part of their own security review — arecurring theme in the checklist above — Knit's security practices aredocumented in full at getknit.dev/security, making it straightforward toinclude in a vendor security assessment.
Does Knit store or share end-user data with third parties?
No. Knit is built as apass-through proxy and does not store a copy of your end users' data on itsservers or share it with any third party. Data is processed in Knit'sapplication server and sent directly to your webhooks via event-based syncs,rather than being retained in a database. This directly addresses one of thebiggest third-party API security concerns covered in this guide — that avendor's data retention practices could expose your users' data even if yourown systems are secure. For security-conscious teams, this no-data-copyarchitecture removes an entire category of risk from the third-party API reviewchecklist.
Have a question that isn'tcovered here? Read all the FAQs in Knit's dedicated post on common API securityFAQs.
Enable maximum security for your API integrations with Knit
If you are dealing with a large number of API integrations and looking for smarter solutions, check out unified API solutions like Knit. Knit ensures that you have access to high quality data faster in the safest way possible.
- Knit is the only unified API in the market that does NOT store a copy of your end user data in its servers or share it with any third party. All of our syncs are event-based and happen via webhooks to ensure that your data is not subjected to any external threats during the transfer. Learn more about Knit's secure data sync here
- Knit complies with industry best practices and security standards. We are SOC2, GDPR and ISO27001 certified and always in the process of adding more security badges to our collection.
- We monitor Knit's infrastructure continuously with the finest intrusion detection systems. Plus, our super responsive support team is available 24*7 across all time zones to make sure if at all a security issue occurs, it is resolved immediately.
We understand how crucial your data is. That's why we are always fine-tuning our security measures to offer maximum protection for your user data. Talk to one of our experts to learn more. If you are ready to build integrations at scale, get your API keys for free
