diff --git a/pkg/api/middleware/auth.go b/pkg/api/middleware/auth.go
index 920674f..2ed8585 100644
--- a/pkg/api/middleware/auth.go
+++ b/pkg/api/middleware/auth.go
@@ -2,7 +2,17 @@ package middleware
 
 import (
 	"context"
+	"crypto"
+	"errors"
+	"fmt"
 	"net/http"
+	"strings"
+	"time"
+
+	"github.com/aykhans/bsky-feedgen/pkg/logger"
+	"github.com/bluesky-social/indigo/atproto/identity"
+	"github.com/bluesky-social/indigo/atproto/syntax"
+	"github.com/golang-jwt/jwt/v5"
 )
 
 const UserDIDKey ContextKey = "user_did"
@@ -16,8 +26,154 @@ func JWTAuthMiddleware(next http.Handler) http.Handler {
 			return
 		}
 
-		// TODO: Add auth verification
-		ctx := context.WithValue(r.Context(), UserDIDKey, "")
+		did, err := ValidateAuth(r.Context(), r)
+		if err != nil {
+			logger.Log.Error(err.Error())
+		}
+		ctx := context.WithValue(r.Context(), UserDIDKey, did)
 		next.ServeHTTP(w, r.WithContext(ctx))
 	})
 }
+
+///////////////////////////////////////////////////
+
+const (
+	authorizationHeaderName        = "Authorization"
+	authorizationHeaderValuePrefix = "Bearer "
+)
+
+// AuthorizationError is a custom error type for authorization failures.
+type AuthorizationError struct {
+	Message string
+	Err     error // Wrapped error
+}
+
+// Error returns the formatted error message.
+func (e *AuthorizationError) Error() string {
+	if e.Err != nil {
+		return fmt.Sprintf("%s: %v", e.Message, e.Err)
+	}
+	return e.Message
+}
+
+// Unwrap returns the wrapped error, allowing for errors.Is and errors.As.
+func (e *AuthorizationError) Unwrap() error {
+	return e.Err
+}
+
+// Global (or dependency-injected) DID resolver with caching.
+var didResolver *identity.CacheDirectory
+
+// init function is called once when the package is initialized.
+func init() {
+	// Initialize the base directory for actual DID resolution.
+	baseDir := identity.BaseDirectory{} // Zero value is usable.
+
+	// Configure cache with appropriate TTLs.
+	// Capacity 0 means unlimited cache size.
+	// hitTTL: 24 hours for successful resolutions.
+	// errTTL: 5 minutes for failed resolutions.
+	// invalidHandleTTL: also 5 minutes for invalid handles.
+	resolver := identity.NewCacheDirectory(
+		&baseDir,
+		0,             // Unlimited capacity
+		24*time.Hour,  // hitTTL
+		5*time.Minute, // errTTL
+		5*time.Minute, // invalidHandleTTL
+	)
+	didResolver = &resolver
+}
+
+// getDIDSigningKey resolves a DID and extracts its public signing key.
+// It leverages indigo's identity package which handles multibase decoding and key parsing.
+func getDIDSigningKey(ctx context.Context, did string) (crypto.PublicKey, error) {
+	atID, err := syntax.ParseAtIdentifier(did)
+	if err != nil {
+		return nil, fmt.Errorf("invalid DID syntax: %w", err)
+	}
+
+	// Use Lookup for bi-directional verification (handle -> DID -> handle).
+	// The `Lookup` method returns an `Identity` struct which contains `PublicKey()` method
+	// to get the signing key.
+	identity, err := didResolver.Lookup(ctx, *atID)
+	if err != nil {
+		return nil, fmt.Errorf("DID resolution failed for %s: %w", did, err)
+	}
+	if identity == nil || identity.DID.String() == "" {
+		return nil, fmt.Errorf("DID resolution returned empty identity for %s", did)
+	}
+
+	// Get the public key using the PublicKey() method from the Identity struct.
+	publicKey, err := identity.PublicKey()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get signing key for DID %s: %w", did, err)
+	}
+
+	return publicKey, nil
+}
+
+// ValidateAuth validates the authorization header and returns the requester's DID.
+// It requires a context.Context for DID resolution to allow for timeouts and cancellation.
+func ValidateAuth(ctx context.Context, r *http.Request) (string, error) {
+	authHeader := r.Header.Get(authorizationHeaderName)
+	if authHeader == "" {
+		return "", &AuthorizationError{Message: "Authorization header is missing"}
+	}
+
+	if !strings.HasPrefix(authHeader, authorizationHeaderValuePrefix) {
+		return "", &AuthorizationError{Message: "Invalid authorization header format"}
+	}
+
+	jwtString := strings.TrimPrefix(authHeader, authorizationHeaderValuePrefix)
+	jwtString = strings.TrimSpace(jwtString)
+
+	// Define a custom claims struct if needed, otherwise use jwt.RegisteredClaims.
+	claims := jwt.RegisteredClaims{}
+
+	// Keyfunc callback to dynamically fetch the public key based on the JWT's issuer (iss).
+	keyFunc := func(token *jwt.Token) (interface{}, error) {
+		// Assert claims to RegisteredClaims to get the issuer (iss).
+		regClaims, ok := token.Claims.(*jwt.RegisteredClaims)
+		if !ok {
+			return nil, fmt.Errorf("invalid JWT claims type")
+		}
+
+		issuerDID := regClaims.Issuer
+		if issuerDID == "" {
+			return nil, fmt.Errorf("JWT 'iss' claim is missing")
+		}
+
+		// Resolve the DID and get the public signing key.
+		publicKey, err := getDIDSigningKey(ctx, issuerDID)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get signing key for DID %s: %w", issuerDID, err)
+		}
+
+		return publicKey, nil
+	}
+
+	token, err := jwt.ParseWithClaims(jwtString, &claims, keyFunc)
+	if err != nil {
+		if errors.Is(err, jwt.ErrTokenSignatureInvalid) {
+			return "", &AuthorizationError{Message: "Invalid signature", Err: err}
+		}
+		if errors.Is(err, jwt.ErrTokenExpired) {
+			return "", &AuthorizationError{Message: "Token expired", Err: err}
+		}
+		if errors.Is(err, jwt.ErrTokenNotValidYet) {
+			return "", &AuthorizationError{Message: "Token not valid yet", Err: err}
+		}
+		if errors.Is(err, jwt.ErrTokenMalformed) {
+			return "", &AuthorizationError{Message: "Malformed token", Err: err}
+		}
+		// Catch other generic parsing or validation errors.
+		return "", &AuthorizationError{Message: "Failed to parse or validate JWT", Err: err}
+	}
+
+	if !token.Valid {
+		return "", &AuthorizationError{Message: "Token is invalid"}
+	}
+
+	// Return the issuer's DID.
+	return claims.Issuer, nil
+}