Fix update token interval calculation. (ydb-platform#3064)

We should chouse min value from expiresIn and RefreshPeriod_, not max one
Also reduce server returned interval by 2 to prevent race at expiring time.

ydb/public/sdk/cpp/client/iam/common/iam.cpp

@@ -56,9 +56,11 @@ class TIAMCredentialsProvider : public ICredentialsProvider {
             if (auto it = respMap.find("expires_in"); it == respMap.end())
                 ythrow yexception() << "Result doesn't contain expires_in";
             else {
-                const TDuration expiresIn = TDuration::Seconds(it->second.GetUInteger());
+                const TDuration expiresIn = TDuration::Seconds(it->second.GetUInteger()) / 2;
 
-                NextTicketUpdate_ = TInstant::Now() + std::max(expiresIn, RefreshPeriod_);
+                const auto interval = std::max(std::min(expiresIn, RefreshPeriod_), TDuration::MilliSeconds(100));
+
+                NextTicketUpdate_ = TInstant::Now() + interval;
             }
         } catch (...) {
         }
@@ -83,4 +85,4 @@ TCredentialsProviderFactoryPtr CreateIamCredentialsProviderFactory(const TIamHos
     return std::make_shared<TIamCredentialsProviderFactory>(params);
 }
 
-}
+}