Add time histogram for getting OBO tokens

server/src/auth/cache-gauge.ts

@@ -1,5 +1,5 @@
 import { proxyRegister } from '@app/prometheus/types';
-import { Counter, Gauge } from 'prom-client';
+import { Counter, Gauge, Histogram } from 'prom-client';
 
 const labelNames = ['hit'] as const;
 
@@ -15,3 +15,10 @@ export const cacheSizeGauge = new Gauge({
   help: 'Number of OBO tokens in the cache.',
   registers: [proxyRegister],
 });
+
+export const oboRequestDuration = new Histogram({
+  name: 'obo_request_duration',
+  help: 'Duration of OBO token requests in milliseconds.',
+  buckets: [0, 10, 100, 200, 300, 400, 500, 600, 800, 900, 1_000],
+  registers: [proxyRegister],
+});

server/src/plugins/obo-token.ts

@@ -5,6 +5,7 @@ import { getLogger } from '@app/logger';
 import { getOnBehalfOfAccessToken } from '@app/auth/on-behalf-of';
 import fastifyPlugin from 'fastify-plugin';
 import { isDeployed } from '@app/config/env';
+import { oboRequestDuration } from '@app/auth/cache-gauge';
 
 const log = getLogger('obo-token-plugin');
 
@@ -75,7 +76,10 @@ const getOboToken: GetOboToken = async (appName, req, reply) => {
         trace_id,
         span_id,
       );
-      reply.addServerTiming('obo_token_middleware', getDuration(oboStart), 'OBO Token Middleware');
+
+      const duration = getDuration(oboStart);
+      oboRequestDuration.observe(duration);
+      reply.addServerTiming('obo_token_middleware', duration, 'OBO Token Middleware');
 
       return oboAccessToken;
     } catch (error) {