When configuring authentication for .NET web applications accessing SQL Server, developers often face the dilemma between Windows Authentication (SSPI) and SQL Server authentication. Let's examine the technical implications of each approach.

SSPI leverages Windows Authentication through a process called security context delegation. In a typical IIS-hosted .NET web app:

// Connection string using SSPI
string connectionString = "Server=myServer;Database=myDB;Integrated Security=True;";

The authentication flow works as:

1. Client browser authenticates with the web server
2. IIS passes the security token to the application
3. Application pool identity or impersonated user accesses SQL Server

The traditional alternative uses explicit credentials:

// SQL Server authentication
string connectionString = "Server=myServer;Database=myDB;User Id=myUser;Password=myPass;";

For web applications, several factors influence the choice:

Security Surface:

With SSPI, compromising the web server means the attacker inherits the application pool identity's permissions. With SQL auth, credentials must be properly secured in configuration files or secret stores.

Connection Pooling:

SSPI connections are pooled per security context, while SQL auth pools connections per connection string. This can affect performance in multi-user scenarios.

Deployment Complexity:

SSPI requires identical Active Directory configuration across all environments and proper SPN setup for Kerberos.

For environments where SSPI is preferred but security is a concern, consider constrained delegation:

// Example of secure connection with encrypted credentials
var builder = new SqlConnectionStringBuilder
{
    DataSource = "prod-sql-cluster",
    InitialCatalog = "AppDB",
    IntegratedSecurity = true,
    Pooling = true,
    ConnectTimeout = 15
};

In high-security environments, a combination of techniques may be optimal:

• Use SSPI for internal service-to-service communication
• Implement SQL auth for web front-ends with credentials stored in Azure Key Vault or similar
• Consider Always Encrypted for sensitive data columns

For ASP.NET Core applications, the configuration might look like:

services.AddDbContext(options => 
    options.UseSqlServer(Configuration.GetConnectionString("SecureConnection"),
    sqlOptions => sqlOptions.EnableRetryOnFailure()));

Regardless of authentication method, implement:

• SQL Server audit policies for login tracking
• Regular credential rotation procedures
• Network segmentation between web and database tiers
• Principle of least privilege for all database accounts

When configuring authentication for .NET web applications connecting to SQL Server, developers often face the dilemma between Windows Authentication (SSPI) and SQL Server Authentication. The core security consideration isn't just about the authentication protocol itself, but the attack surface and potential privilege escalation paths.

While Integrated Security (SSPI) appears more secure on surface because it eliminates password storage, it creates potential vulnerabilities in web scenarios:

// Example vulnerable connection string
string connectionString = "Server=myServer;Database=myDB;Trusted_Connection=True;";

The machine account context becomes the single point of failure. If an attacker compromises the web server, they can:

• Perform lateral movement using the machine account
• Access any resource the application pool identity can access
• Potentially escalate privileges within the domain

A more secure pattern would combine multiple security layers:

// Recommended approach with connection pooling and limited SQL login
string connectionString = "Server=myServer;Database=myDB;User Id=webapp_user;Password=Complex@Password123;"
                         + "Pooling=true;Max Pool Size=100;Connection Timeout=30;";

When using SQL Authentication in web apps:

1. Store credentials securely using DPAPI or Azure Key Vault
2. Implement connection pooling with reasonable limits
3. Apply the principle of least privilege to the SQL login
4. Enable encrypted connections (TLS 1.2+)

Regardless of authentication method, implement comprehensive logging:

-- SQL Server audit configuration
CREATE SERVER AUDIT WebApp_Audit
TO FILE (FILEPATH = 'C:\Audits\')
WITH (QUEUE_DELAY = 1000, ON_FAILURE = CONTINUE);

CREATE DATABASE AUDIT SPECIFICATION WebApp_DB_Audit
FOR SERVER AUDIT WebApp_Audit
ADD (SELECT, INSERT, UPDATE, DELETE ON SCHEMA::dbo BY public);

For highly secure environments consider:

• Managed identities in Azure
• Group Managed Service Accounts (gMSA)
• Certificate-based authentication
• Short-lived tokens via OAuth