Demonstrate OTLP exporter programmatic authentication

doc-snippets/configuration/src/main/java/otel/OtlpAuthenticationConfig.java

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+package otel;
+
+import io.opentelemetry.exporter.otlp.http.logs.OtlpHttpLogRecordExporter;
+import io.opentelemetry.exporter.otlp.http.metrics.OtlpHttpMetricExporter;
+import io.opentelemetry.exporter.otlp.http.trace.OtlpHttpSpanExporter;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.Collections;
+import java.util.Map;
+import java.util.function.Supplier;
+
+public class OtlpAuthenticationConfig {
+  public static void staticAuthenticationHeader(String endpoint) {
+    // If the OTLP destination accepts a static, long-lived authentication header like an API key,
+    // set it as a header.
+    // This reads the API key from the OTLP_API_KEY env var to avoid hard coding the secret in
+    // source code.
+    String apiKeyHeaderName = "api-key";
+    String apiKeyHeaderValue = System.getenv("OTLP_API_KEY");
+
+    // Initialize OTLP Span, Metric, and LogRecord exporters using a similar pattern
+    OtlpHttpSpanExporter spanExporter =
+        OtlpHttpSpanExporter.builder()
+            .setEndpoint(endpoint)
+            .addHeader(apiKeyHeaderName, apiKeyHeaderValue)
+            .build();
+    OtlpHttpMetricExporter metricExporter =
+        OtlpHttpMetricExporter.builder()
+            .setEndpoint(endpoint)
+            .addHeader(apiKeyHeaderName, apiKeyHeaderValue)
+            .build();
+    OtlpHttpLogRecordExporter logRecordExporter =
+        OtlpHttpLogRecordExporter.builder()
+            .setEndpoint(endpoint)
+            .addHeader(apiKeyHeaderName, apiKeyHeaderValue)
+            .build();
+  }
+
+  public static void dynamicAuthenticationHeader(String endpoint) {
+    // If the OTLP destination requires a dynamic authentication header, such as a JWT which needs
+    // to be periodically refreshed, use a header supplier.
+    // Here we implement a simple supplier which adds a header of the form "Authorization: Bearer
+    // <token>", where <token> is fetched from refreshBearerToken every 10 minutes.
+    String username = System.getenv("OTLP_USERNAME");
+    String password = System.getenv("OTLP_PASSWORD");
+    Supplier<Map<String, String>> supplier =
+        new AuthHeaderSupplier(() -> refreshToken(username, password), Duration.ofMinutes(10));
+
+    // Initialize OTLP Span, Metric, and LogRecord exporters using a similar pattern
+    OtlpHttpSpanExporter spanExporter =
+        OtlpHttpSpanExporter.builder().setEndpoint(endpoint).setHeaders(supplier).build();
+    OtlpHttpMetricExporter metricExporter =
+        OtlpHttpMetricExporter.builder().setEndpoint(endpoint).setHeaders(supplier).build();
+    OtlpHttpLogRecordExporter logRecordExporter =
+        OtlpHttpLogRecordExporter.builder().setEndpoint(endpoint).setHeaders(supplier).build();
+  }
+
+  private static class AuthHeaderSupplier implements Supplier<Map<String, String>> {
+    private final Supplier<String> tokenRefresher;
+    private final Duration tokenRefreshInterval;
+    private Instant refreshedAt = Instant.ofEpochMilli(0);
+    private String currentTokenValue;
+
+    private AuthHeaderSupplier(Supplier<String> tokenRefresher, Duration tokenRefreshInterval) {
+      this.tokenRefresher = tokenRefresher;
+      this.tokenRefreshInterval = tokenRefreshInterval;
+    }
+
+    @Override
+    public Map<String, String> get() {
+      return Collections.singletonMap("Authorization", "Bearer " + getToken());
+    }
+
+    private synchronized String getToken() {
+      Instant now = Instant.now();
+      if (currentTokenValue == null || now.isAfter(refreshedAt.plus(tokenRefreshInterval))) {
+        currentTokenValue = tokenRefresher.get();
+        refreshedAt = now;
+      }
+      return currentTokenValue;
+    }
+  }
+
+  private static String refreshToken(String username, String password) {
+    // For a production scenario, this would be replaced with out-of-band request to exchange
+    // username / password for bearer token.
+    return "abc123";
+  }
+}