Do you experience Portainer's OAuth login functionality, returning the error "Unable to login via OAuth." This unexpected disruption, which emerged without prior warning, immediately impacted user access. Prior to this failure, OAuth logins functioned flawlessly. A local administrative login was successfully established to investigate the root cause, and a thorough review of the authorization configuration was performed, revealing no apparent misconfigurations.
The problem manifested as an inability to authenticate via OAuth, a stark contrast to the expected behavior of seamless OAuth login. To reproduce the issue, one simply needed to visit the Portainer domain and attempt to log in using Single Sign-On (SSO).
Analyzing the Portainer logs provided crucial insight into the failure. Each failed OAuth login attempt generated a consistent error message:
2025/02/26 03:45PM ERR github.com/portainer/portainer-ee/api/oauth/oauth.go:39 > failed retrieving resource | error="Get "https://domain.com/auth/realms/REALMNAME/protocol/openid-connect/userinfo": http2: server sent GOAWAY and closed the connection; LastStreamID=3, ErrCode=ENHANCE_YOUR_CALM, debug=""
This error clearly indicated a problem with the communication between Portainer and the authentication server (https://domain.com). The error message "http2: server sent GOAWAY and closed the connection" points to an HTTP/2 protocol issue, specifically a GOAWAY frame sent by the server, abruptly terminating the connection. The ErrCode=ENHANCE_YOUR_CALM suggests a potential issue with the request size or header information exceeding server limitations.
Further investigation revealed that the underlying cause was related to changes in the access token size. The authentication server began issuing access tokens significantly larger than previously encountered. This size increase caused Nginx, acting as a reverse proxy, to reject the requests due to exceeding its configured limits for HTTP/2 header and field sizes.
The solution involved adjusting Nginx's configuration to accommodate these larger access tokens. Specifically, the following directives were added to the Nginx configuration file:
# Increase the maximum size of HTTP/2 headers. The previous limit was likely too small for the larger access tokens.
http2_max_header_size 128k;
# Increase the maximum size of individual HTTP/2 fields. This ensures that even large individual header fields within the overall header size can be processed.
http2_max_field_size 64k;
These changes effectively increased the maximum allowable size of both HTTP/2 headers and individual header fields, resolving the issue with oversized access tokens. The values 128k and 64k were chosen to provide sufficient headroom while remaining within reasonable limits for resource consumption. Smaller values could be tried for optimization, but these values should adequately address the issue unless extremely large access tokens are being issued. Carefully monitor the server logs for any errors or warnings indicating resource exhaustion after modifying these parameters.
A secondary, less obvious issue also contributed to the authentication failure. The initial Portainer upstream configuration used localhost:port to define the upstream server. This configuration, unexpectedly, resulted in connections being routed over IPv6, even though the IPv6 address was not accessible. The solution here was to explicitly specify the IPv4 loopback address using 127.0.0.1:port. This ensured that all connections were routed to the correct, accessible IPv4 interface.
Replacing localhost:port with 127.0.0.1:port in the upstream configuration resolved this problem. Using the loopback address guarantees that the connection remains within the local system, preventing any unintended routing issues. This is a crucial best practice to ensure consistent behavior and prevent unexpected behavior arising from network configuration differences. Using localhost can be ambiguous and prone to misinterpretation by different network stacks. Always specify IPv4 or IPv6 explicitly to avoid such ambiguities.
The combined resolution – adjusting the Nginx http2_max_header_size and http2_max_field_size directives and explicitly specifying the IPv4 loopback address in the upstream configuration – fully restored OAuth login functionality in Portainer. This experience underscores the importance of diligently examining both application logs and network configurations when troubleshooting authentication failures. The seemingly unrelated issues, larger-than-expected tokens and IPv6 routing issues, highlighted the necessity of a thorough approach to debugging in complex systems. Careful analysis of seemingly insignificant details is crucial in uncovering the root cause of system failures. This incident serves as a practical demonstration of how seemingly small configurations can result in major disruptions and highlights the importance of regular reviews and testing.
The combined resolution, a seemingly simple adjustment to Nginx and a clarification of the upstream configuration, highlighted the criticality of meticulously analyzing server logs and network configurations during troubleshooting. This case study reinforces the importance of a thorough approach, emphasizing that seemingly minor details can sometimes lead to major disruptions.
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