failed to build call credentials from bootstrap for

Error message

failed to build call credentials from bootstrap for %q: %v

What it means

Returned when a call credentials plugin's Build() fails while parsing a bootstrap server config. This path only runs when the GRPC_XDS_BOOTSTRAP_CALL_CREDENTIALS feature flag (envconfig.XDSBootstrapCallCredsEnabled) is on. The credential type name is printed along with the underlying error.

Solutions

Confirm whether you intend to enable xDS call credentials (env var GRPC_XDS_BOOTSTRAP_CALL_CREDENTIALS); if not, unset it.
Inspect the underlying %v to see which call creds plugin and which constraint failed.
For jwtcreds: ensure jwt_token_file points to a readable, valid JWT file.
Validate the call_creds config block matches gRFC A97.

Example fix

// before: call creds enabled but jwt_token_file invalid
"call_creds":[{"type":"jwt","config":{"jwt_token_file":""}}]

// after
"call_creds":[{"type":"jwt","config":{"jwt_token_file":"/var/secrets/token.jwt"}}]

Defensive patterns

Strategy: validation

Validate before calling

// Only enable xDS call credentials when config is complete.
func callCredsReady(entries []callCredsEntry) bool {
    if !osvHasFlag("GRPC_XDS_BOOTSTRAP_CALL_CREDENTIALS") {
        return true // feature off, error cannot fire
    }
    for _, e := range entries {
        if e.Type == "jwt" && e.JWTTokenFile == "" {
            return false
        }
    }
    return true
}

Try / catch

if _, err := bootstrap.NewConfigFromContents(data); err != nil {
    if strings.Contains(err.Error(), "failed to build call credentials") {
        // either fix the call_creds config or unset the call-creds feature flag.
    }
}

Prevention

Only set GRPC_XDS_BOOTSTRAP_CALL_CREDENTIALS when the call_creds config is fully populated.
Validate JWT token files at deploy time.
Document which env vars gate this code path.

When it happens

Trigger: Triggered at bootstrap.go:391 when c.Build(cfg.Config) errors for a registered call credentials plugin. Example: the jwtcreds plugin fails because the JWT token file path is invalid or empty.

Common situations: Feature flag enabled but call_creds config is incomplete; jwt_token_file path missing/unreadable; call creds plugin name typo causing Build to receive wrong config shape.

Related errors

AI-assisted analysis of grpc/grpc-go@0c51461d27 (2026-08-11). Data as JSON: /api/errors/ef7a547458024ead. Report an issue: GitHub.

Appendix: source

Thrown at internal/xds/bootstrap/bootstrap.go:391

			sc.extraDialOptions = d.DialOptions()
		}
		sc.cleanups = append(sc.cleanups, cancel)
		break
	}

	if envconfig.XDSBootstrapCallCredsEnabled {
		// Process call credentials - unlike channel creds, we use ALL supported
		// types. Also, call credentials are optional as per gRFC A97.
		for _, cfg := range server.CallCredsConfigs {
			c := bootstrap.GetCallCredentials(cfg.Type)
			if c == nil {
				// Skip unsupported call credential types (don't fail bootstrap).
				continue
			}
			callCreds, cancel, err := c.Build(cfg.Config)
			if err != nil {
				// Call credential validation failed - this should fail bootstrap.
				return fmt.Errorf("failed to build call credentials from bootstrap for %q: %v", cfg.Type, err)
			}
			sc.selectedCallCreds = append(sc.selectedCallCreds, callCreds)
			sc.extraDialOptions = append(sc.extraDialOptions, grpc.WithPerRPCCredentials(callCreds))
			sc.cleanups = append(sc.cleanups, cancel)
		}
	}

	if sc.serverURI == "" {
		return fmt.Errorf("xds: `server_uri` field in server config cannot be empty: %s", string(data))
	}
	if sc.credsDialOption == nil {
		return fmt.Errorf("xds: `channel_creds` field in server config cannot be empty: %s", string(data))
	}
	return nil
}

// ServerConfigTestingOptions specifies options for creating a new ServerConfig
// for testing purposes.

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