define ocis_url as a shared option in ocis-pkg/config

proxy/pkg/command/server.go

@@ -52,6 +52,14 @@ func Server(cfg *config.Config) *cli.Command {
 				cfg.PreSignedURL.AllowedHTTPMethods = ctx.StringSlice("presignedurl-allow-method")
 			}
 
+			// we need a starting point to compare the default config values to determine if the outcome of ParseConfig
+			// modified a value that should be shared just because it is present in the ocis.yaml file.
+			defaultConfig := config.DefaultConfig()
+
+			if cfg.OcisURL != "" && cfg.OIDC.Issuer == defaultConfig.OIDC.Issuer {
+				cfg.OIDC.Issuer = cfg.OcisURL
+			}
+
 			if err := loadUserAgent(ctx, cfg); err != nil {
 				return err
 			}

proxy/pkg/config/config.go

@@ -105,6 +105,8 @@ type Cache struct {
 
 // Config combines all available configuration parts.
 type Config struct {
+	OcisURL string
+
 	File                  string          `mapstructure:"file"`
 	Log                   Log             `mapstructure:"log"`
 	Debug                 Debug           `mapstructure:"debug"`

proxy/pkg/config/mappings.go

@@ -123,7 +123,7 @@ func structMappings(cfg *Config) []mapping {
 			Destination: &cfg.InsecureBackends,
 		},
 		{
-			EnvVars:     []string{"PROXY_OIDC_ISSUER", "OCIS_URL"}, // PROXY_OIDC_ISSUER takes precedence over OCIS_URL
+			EnvVars:     []string{"PROXY_OIDC_ISSUER"},
 			Destination: &cfg.OIDC.Issuer,
 		},
 		{