Introduction to Client Authorization

Client authorization involves a combination of authentication, which verifies the client’s identity, and authorization, which ensures the client has the appropriate permissions for the requested resources. These processes are facilitated by various mechanisms, including API keys, OAuth 2.0, bearer tokens, basic authentication, and JSON Web Tokens (JWT). Each method has its strengths and is suited for specific use cases, as we will explore in detail.

What is Client Authorization?

At its core, client authorization is a security mechanism designed to validate whether a client has the necessary permissions to access particular API endpoints. This validation ensures sensitive data is protected, server resources are not misused, and interactions are compliant with security policies.

API keys are one of the simplest authorization mechanisms, where a unique string of characters is issued to each client. These keys are often included in API requests to verify the client’s identity. While easy to implement, API keys alone may not provide adequate security, especially if they are exposed or mismanaged.

OAuth 2.0 is a more robust framework that uses access tokens to grant clients permission to access resources. This protocol is widely adopted in scenarios requiring third-party integrations, such as logging into an application using social media accounts. OAuth 2.0 supports granular access control, allowing specific permissions to be granted for different actions.

Bearer tokens, a simpler form of token-based authentication, are used to validate requests during a session. These tokens are typically included in the HTTP Authorization header. While convenient, they must be carefully managed to avoid unauthorized reuse. In contrast, basic authentication involves sending a username and password encoded in Base64, making it straightforward but less secure if used without HTTPS.

JSON Web Tokens (JWT) are a popular choice for modern web applications, providing a compact, self-contained format for transmitting claims between parties. A JWT consists of three parts: the header, which specifies the token type and signing algorithm; the payload, which contains the claims; and the signature, which verifies the token’s integrity. This format enables quick verification and supports stateless authentication, where the server does not need to store session information.

OAuth 2.0 Client Credentials Grant

The OAuth 2.0 Client Credentials Grant is a widely used authorization flow for machine-to-machine (M2M) authentication. Unlike other OAuth flows that require user involvement, this grant type is designed specifically for applications that need to authenticate themselves when requesting access to API resources. It is commonly used in backend services, microservices communication, and API integrations where user authentication is unnecessary.

Understanding the Client Credentials Grant Flow

In this authorization flow, a client application—such as a backend service—requests access to a protected resource by presenting its own credentials (client ID and client secret) to an authorization server. The authorization server validates these credentials and issues an access token, which the client can then use to authenticate API requests. The key steps in the Client Credentials Grant flow include:

Client Authentication: The client sends its credentials (client ID and secret) in a secure request to the authorization server’s token endpoint.
Token Issuance: If the provided credentials are valid, the authorization server responds with an access token.
Accessing Protected Resources: The client includes the issued access token in API requests, allowing it to access protected resources.
Token Expiry and Renewal: Since access tokens have a limited lifespan, the client must periodically obtain a new token by repeating the authentication process.

How OAuth 2.0 Enhances Security in Client Authentication

The Client Credentials Grant improves security in several ways:

Prevents Credential Sharing: Applications authenticate using their own credentials rather than user passwords, reducing the risk of credential leaks.
Enables Fine-Grained Access Control: The authorization server can issue tokens with specific scopes, restricting API access to only necessary operations.
Uses Short-Lived Tokens: Access tokens typically expire within a short time window, minimizing risks associated with stolen credentials.
Supports Encrypted Communication: OAuth 2.0 mandates the use of HTTPS to protect token exchange and prevent interception by malicious actors.

Real-World Scenarios: How Client Authorization Works in Practice

Use Case 1: Automating Invoice Processing Between Two Backend Services

Scenario

A financial software system includes a billing service and an accounting service. The billing service needs to securely send invoice data to the accounting service using an internal API.

Step-by-Step Breakdown
- Client Authentication
  - The billing service authenticates with the authorization server using its client ID and client secret.
  - It receives an access token via the OAuth 2.0 Client Credentials Grant.
- Authorization Request
  - The billing service sends a POST request to the accounting service’s API, including the bearer token in the Authorization header.
- Access Enforcement
  - The accounting service validates the token and checks whether it includes the write:invoices scope.
  - If valid, it processes and stores the invoice data.

Use Case 2: Internal Tool Accessing Company APIs with Scoped Permissions

Scenario

An internal dashboard tool used by HR needs to fetch employee performance data from various microservices without user interaction.

Step-by-Step Breakdown
- Client Authentication
  - The dashboard authenticates to the authorization server using its registered credentials.
  - An access token scoped to read:performance and read:attendance is issued.
- Authorization Request
  - The dashboard includes the token in requests to each microservice.
- Access Enforcement
  - Each microservice validates the token and checks that the requested operation matches the granted scopes.
  - Unauthorized operations are denied to uphold least-privilege access.

Comparison with OIDC

OpenID Connect (OIDC) is an authentication protocol built on top of OAuth 2.0. While OAuth 2.0 is designed primarily for authorization—allowing applications to securely access APIs—OIDC extends OAuth by providing authentication capabilities, enabling applications to verify user identities. OIDC standardizes identity verification across applications and platforms, making it particularly valuable in single sign-on (SSO) and federated authentication systems.

How OIDC Works

OIDC builds on OAuth 2.0 by introducing an ID token, which contains structured information about the authenticated user. The ID token is issued alongside an access token and is signed by the identity provider (IdP) to ensure its authenticity. The OIDC flow typically involves:

User Authentication: The user logs in to the identity provider (e.g., Google, Microsoft, or an enterprise IdP).
Authorization Server Validation: The identity provider authenticates the user and issues an ID token.
Token Verification: The application verifies the ID token’s signature and extracts user identity information.
Access Control Enforcement: Based on the identity information, the application grants or denies access to resources.

Key Differences Between OAuth 2.0 and OIDC

Purpose: OAuth 2.0 is used for authorization, ensuring clients can access resources on behalf of a user or themselves. OIDC, on the other hand, is used for authentication, allowing applications to confirm a user identity.
ID Token vs. Access Token: OIDC introduces an ID token, which contains user identity information (e.g., name, email, and authentication method). OAuth 2.0, however, only issues access tokens for resource access.
User Involvement: OAuth 2.0 Client Credentials Grant does not require user interaction, as it is designed for machine-to-machine communication. OIDC typically involves user authentication, such as login prompts.
Scopes and Claims: OIDC defines standard scopes (openid, profile, email) that return user identity claims, whereas OAuth 2.0 access tokens are used solely for authorization.

5. Security and Trust Model: OIDC ensures authentication is handled by a trusted identity provider, reducing the need for applications to store sensitive credentials.

Use Cases for OIDC

OIDC is widely used in scenarios where user authentication and identity verification are required:

Single Sign-On (SSO): Users authenticate once and gain access to multiple applications without re-entering credentials.
Federated Identity Management: Organizations integrate multiple identity providers to allow seamless authentication across systems.
Social Logins: Users authenticate with their existing credentials from platforms like Google, Facebook, or LinkedIn.
Enterprise Authentication: Large enterprises use OIDC to centralize authentication through identity providers like Microsoft Azure AD or Okta.

When to Use OAuth 2.0 vs. OIDC

Use OAuth 2.0 Client Credentials Grant for service-to-service authentication, backend communication, and automated workflows.
Use OIDC when authentication and identity verification are required, such as for login-based applications, social logins, and SSO solutions.

By understanding the differences between OAuth 2.0 and OIDC, organizations can make informed decisions on the appropriate authentication and authorization mechanisms for their applications.

Key Concepts in Secure API Access

Understanding the distinction between authentication and authorization is crucial. Authentication confirms the client’s identity, while authorization determines the resources and actions the client is allowed to access. These two processes work together to establish a secure API interaction.

Tokens are central to secure API access. Access tokens, which are often short-lived, grant temporary access to specific resources. Refresh tokens, in contrast, are used to obtain new access tokens without requiring re-authentication. This approach balances security with usability, reducing the need for frequent logins.

To ensure the stability and security of APIs, rate limiting and throttling are often implemented. Rate limiting restricts the number of requests a client can make within a given timeframe, while throttling temporarily blocks clients exceeding this limit. These measures prevent abuse, protect server resources, and ensure fair usage among clients.

Proxy caching further enhances API performance by storing frequently accessed responses. This approach reduces server load and improves response times for clients, especially in high-traffic scenarios.

How it works in digiRunner

Client authorization is crucial for securing API communication, ensuring that only authenticated and authorized clients can access your APIs. This guide walks through the steps to implement client authorization in digiRunner, based on the official documentation available at digiRunner Docs.

I. Securing Server-to-Server API Communication

Step 1: Configure OAuth 2.0 for Client Authorization

Navigate to API Gateway Settings: Log in to digiRunner and go to the API Gateway section.
Enable OAuth 2.0: Under the Authorization settings, enable OAuth 2.0 and configure client credentials.
Register Clients: Create and register client applications with unique client IDs and secrets.
Generate Tokens: Clients must authenticate and obtain tokens from the authorization server before making API requests.
Attach Tokens to Requests: Ensure API consumers include the bearer token in the Authorization header when calling secured APIs.

Step 2: Define Scope and Permission Management

Create API Scopes: Define specific scopes for different API endpoints.
Assign Scopes to Clients: Restrict access to APIs based on assigned scopes.
Validate Scope on API Requests: Configure the API Gateway to validate the scope and deny unauthorized requests.

Step 3: Configure API Gateway for Authorization

Enable Authorization Middleware: Activate built-in authorization middleware in digiRunner’s API Gateway.
Set Up Role-Based Access Control (RBAC): Assign roles to API clients and specify permitted actions.
Monitor API Traffic: Use digiRunner’s analytics dashboard to track authorization events.

II. Enhancing Security in Client Authorization

Step 4: Implement Client Authentication Using Mutual TLS (mTLS)

Enable mTLS in API Gateway: Configure the API Gateway to require mutual TLS for client authentication.
Upload Client Certificates: Register trusted client certificates within digiRunner.
Enforce Certificate Validation: Ensure that API requests without a valid client certificate are rejected.

Step 5: Apply IP Whitelisting and Rate Limiting

Define Allowed IP Ranges: Restrict API access to specific IP addresses.
Configure Rate Limits: Set up request rate limits to prevent API abuse.
Monitor Traffic Patterns: Regularly review access logs to detect anomalies.

Step 6: Implement Logging and Auditing

Enable API Logs: Capture request and response logs for auditing purposes.
Monitor Access Attempts: Track failed and successful authorization attempts.
Set Up Alerts: Configure security alerts for suspicious activities.

Key Considerations & Best Practices

Use Strong Client Secrets: Rotate client secrets regularly to minimize security risks.
Enforce Least Privilege: Assign the minimum necessary scopes and permissions to each client.
Automate Security Checks: Leverage automation to enforce security policies and detect anomalies.
Regularly Review Logs: Periodic security audits help ensure compliance and identify potential threats.

By following these steps, you can effectively implement client authorization and enhance security in digiRunner. For more details, refer to the official documentation at digiRunner Docs.

Best Practices for Client Authorization

Securing client authorization is crucial for protecting APIs from unauthorized access. Implementing best practices ensures security, scalability, and proper access control across different authorization mechanisms such as OAuth 2.0, API Keys, and JWT (JSON Web Token).

1. Choose the Right Authorization Mechanism

Why?

Different use cases require different authorization methods to balance security and usability.

How?

OAuth 2.0 + OpenID Connect (OIDC) → Suitable for user authentication, including Single Sign-On (SSO).
OAuth 2.0 Client Credentials Grant → Best for machine-to-machine (M2M) communication.
API Key → Works for simple API access control but should be combined with additional security measures like IP restrictions.
JWT (JSON Web Token) → Ideal for internal security communication in distributed architectures (e.g., microservices).

In digiRunner:

Implementation: digiRunner supports multiple authorization methods, including OAuth 2.0 (Authorization Code, Client Credentials), API Key, and JWT, allowing users to choose the most suitable approach based on their use case.
Reference: Client Authorization and Calling APIs

2. Secure Client Credentials

Why?

Exposing client credentials in frontend applications increases security risks and potential credential leaks.

How?

Never expose client_secret, API keys, or tokens in JavaScript, HTML, or mobile apps.
Use backend services to securely manage credentials.
Store client_secret securely using environment variables or secret management services (e.g., AWS Secrets Manager).

In digiRunner:

Implementation: Client secrets in digiRunner are securely stored and managed through the Admin Console. Secrets should only be configured server-side and never exposed to frontend apps.
Reference: API Client

3. Use Short-Lived Tokens to Minimize Risk

Why?

Short-lived tokens reduce the impact of token leaks and unauthorized use.

How?

Set access token expiration times to short durations (e.g., 5–15 minutes).
Implement refresh tokens to allow clients to request new tokens without requiring user re-authentication.
Avoid long-lived API keys; if necessary, enforce regular rotation policies.

In digiRunner:

Implementation: Access and refresh token lifetimes can be configured per API Client. Admins are encouraged to use short expiration times and enable refresh tokens for long-term sessions.
Reference: Token Lifecycle Management Mechanism

4. Restrict API Access Using Scopes & Permissions

Why?

Applying the principle of least privilege ensures APIs only grant the necessary access, preventing excessive authorization.

How?

Use scopes to define permissions. Example:

{

"sub": "1234567890",

"scope": "read:users write:orders"

}

Avoid issuing high-privilege tokens unless absolutely necessary.
Ensure role-based access control (RBAC) is enforced at the API level.

In digiRunner:

Implementation: You can define custom scopes and associate them with API Clients to control what resources can be accessed. Role-based access is also supported through token claims.
Reference: API Scope

5. Implement Strong Authentication (MFA)

Why?

Multi-Factor Authentication (MFA) enhances security by requiring additional verification beyond just a password.

How?

Enforce MFA for high-security applications.
When using OAuth 2.0 Authorization Code Flow, enable PKCE (Proof Key for Code Exchange) to prevent authorization code interception attacks.

In digiRunner:

Implementation: While MFA is enforced at the identity provider level (e.g., Azure AD, Google), digiRunner integrates with OIDC-compliant IdPs that support MFA for added protection.
Reference: OpenID Connect (OIDC) Mode

6. Protect API from Credential Exposure Attacks

Why?

Mitigating attack vectors such as Man-in-the-Middle (MITM), brute force, and credential stuffing improves API security.

How?

Enforce HTTPS to prevent MITM attacks.
Implement rate limiting to restrict excessive requests from a single client and prevent brute-force attacks.
Use IP Whitelisting & Client Allowlists to restrict API access to specific trusted IP addresses.
Monitor API behavior for suspicious activity, such as:
- If an API key is used from multiple locations within a short timeframe, consider revoking it.
- Use a Web Application Firewall (WAF) to detect and block malicious requests.

In digiRunner:

Implementation: All credential exchanges and token issuances in digiRunner are conducted over HTTPS. IP whitelisting and rate limiting can also be configured per API Client.
Reference: API Client

7. Regularly Rotate Credentials & Audit Access Logs

Why?

Regular credential rotation and access monitoring help detect anomalies and prevent long-term credential leaks.

How?

Enforce regular API key and client secret rotation.
Log and monitor API access activities, including:
- API requests
- Logins
- Token exchanges
Use SIEM (Security Information & Event Management) solutions to detect and respond to anomalies.

In digiRunner:

Implementation: Client credentials can be regenerated and rotated through the Admin Console. Additionally, access logs and audit trails are available for monitoring usage and detecting anomalies.
Reference: API Client

By following these best practices, you can ensure secure, scalable, and well-controlled client authorization for your APIs.

Conclusion

In this course, we have explored the essential aspects of Client Authorization within digiRunner. Starting from a high-level overview, we examined the importance of authorization in API security and compliance. We then dived into how digiRunner implements client authorization, emphasizing its intuitive UI, support for multiple authorization mechanisms, and integration with OAuth2 standards.

Finally, we discussed best practices, including managing credentials securely, regularly reviewing access rights, and employing role-based access controls to minimize risk.

By understanding and applying these principles, users can ensure that their API services remain protected, scalable, and in compliance with security standards. This not only strengthens the technical robustness of the platform but also builds trust with clients and partners.

We encourage you to continue exploring the full capabilities of digiRunner and apply the knowledge from this course to optimize your API management strategy.

digiRunner Playbook III: Client Authorization