Cannot modify header information - headers already sent

[solracsf]

On NC 24.0.8, with latest app version (5.1.2):

{
  "reqId": "rwC2CbWZ4phfcLjQujFW",
  "level": 3,
  "time": "2023-01-13T13:51:29+01:00",
  "remoteAddr": "27.11.2.18",
  "user": "--",
  "app": "PHP",
  "method": "POST",
  "url": "/apps/user_saml/saml/acs",
  "message": "Cannot modify header information - headers already sent by (output started at /var/www/nextcloud/apps/user_saml/3rdparty/vendor/onelogin/php-saml/src/Saml2/Response.php:452) at /var/www/nextcloud/lib/private/AppFramework/Http/Output.php#70",
  "userAgent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/109.0.0.0 Safari/537.36",
  "version": "24.0.8.2",
  "exception": {
    "Exception": "Error",
    "Message": "Cannot modify header information - headers already sent by (output started at /var/www/nextcloud/apps/user_saml/3rdparty/vendor/onelogin/php-saml/src/Saml2/Response.php:452) at /var/www/nextcloud/lib/private/AppFramework/Http/Output.php#70",
    "Code": 0,
    "Trace": [
      {
        "function": "onAll",
        "class": "OC\\Log\\ErrorHandler",
        "type": "::",
        "args": [
          2,
          "Cannot modify header information - headers already sent by (output started at /var/www/nextcloud/apps/user_saml/3rdparty/vendor/onelogin/php-saml/src/Saml2/Response.php:452)",
          "/var/www/nextcloud/lib/private/AppFramework/Http/Output.php",
          70
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/AppFramework/Http/Output.php",
        "line": 70,
        "function": "header",
        "args": [
          "Content-Length: 0"
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/AppFramework/App.php",
        "line": 231,
        "function": "setHeader",
        "class": "OC\\AppFramework\\Http\\Output",
        "type": "->",
        "args": [
          "Content-Length: 0"
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/Route/Router.php",
        "line": 298,
        "function": "main",
        "class": "OC\\AppFramework\\App",
        "type": "::",
        "args": [
          "OCA\\User_SAML\\Controller\\SAMLController",
          "assertionConsumerService",
          {
            "__class__": "OC\\AppFramework\\DependencyInjection\\DIContainer"
          },
          [
            "user_saml.SAML.assertionConsumerService"
          ]
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/base.php",
        "line": 1030,
        "function": "match",
        "class": "OC\\Route\\Router",
        "type": "->",
        "args": [
          "/apps/user_saml/saml/acs"
        ]
      },
      {
        "file": "/var/www/nextcloud/index.php",
        "line": 36,
        "function": "handleRequest",
        "class": "OC",
        "type": "::",
        "args": []
      }
    ],
    "File": "/var/www/nextcloud/lib/private/Log/ErrorHandler.php",
    "Line": 99,
    "CustomMessage": "--"
  },
  "id": "63c154ce1fe4a"
}

followed by

{
  "reqId": "VOObLzEFXnm13RmPqfmB",
  "level": 3,
  "time": "2023-01-13T13:51:49+01:00",
  "remoteAddr": "21.17.2.18",
  "user": "--",
  "app": "PHP",
  "method": "GET",
  "url": "/apps/user_saml/saml/sls?requesttoken=bf9JX1DN2xR4opGtLR73N9/iX9nEJKRVw12W3GP9X7w%3D:W7kNNj6EriJL9efufUyTda%2BTa%2BzrXsAMihmhkwCJD%2Bk%3D",
  "message": "session_start(): Ignoring session_start() because a session is already active at /var/www/nextcloud/lib/private/Session/Internal.php#208",
  "userAgent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/109.0.0.0 Safari/537.36",
  "version": "24.0.8.2",
  "exception": {
    "Exception": "Error",
    "Message": "session_start(): Ignoring session_start() because a session is already active at /var/www/nextcloud/lib/private/Session/Internal.php#208",
    "Code": 0,
    "Trace": [
      {a
        "function": "onAll",
        "class": "OC\\Log\\ErrorHandler",
        "type": "::",
        "args": [
          8,
          "session_start(): Ignoring session_start() because a session is already active",
          "/var/www/nextcloud/lib/private/Session/Internal.php",
          208
        ]
      },
      {
        "function": "session_start",
        "args": [
          [
            "Lax"
          ]
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/Session/Internal.php",
        "line": 208,
        "function": "call_user_func_array",
        "args": [
          "session_start",
          [
            [
              "Lax"
            ]
          ]
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/Session/Internal.php",
        "line": 218,
        "function": "invoke",
        "class": "OC\\Session\\Internal",
        "type": "->",
        "args": [
          "session_start",
          [
            [
              "Lax"
            ]
          ],
          true
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/Session/Internal.php",
        "line": 106,
        "function": "startSession",
        "class": "OC\\Session\\Internal",
        "type": "->",
        "args": [
          true
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/Session/CryptoSessionData.php",
        "line": 149,
        "function": "clear",
        "class": "OC\\Session\\Internal",
        "type": "->",
        "args": []
      },
      {
        "file": "/var/www/nextcloud/lib/private/User/Session.php",
        "line": 939,
        "function": "clear",
        "class": "OC\\Session\\CryptoSessionData",
        "type": "->",
        "args": []
      },
      {
        "file": "/var/www/nextcloud/apps/user_saml/lib/Controller/SAMLController.php",
        "line": 495,
        "function": "logout",
        "class": "OC\\User\\Session",
        "type": "->",
        "args": []
      },
      {
        "file": "/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php",
        "line": 225,
        "function": "singleLogoutService",
        "class": "OCA\\User_SAML\\Controller\\SAMLController",
        "type": "->",
        "args": []
      },
      {
        "file": "/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php",
        "line": 133,
        "function": "executeController",
        "class": "OC\\AppFramework\\Http\\Dispatcher",
        "type": "->",
        "args": [
          {
            "__class__": "OCA\\User_SAML\\Controller\\SAMLController"
          },
          "singleLogoutService"
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/AppFramework/App.php",
        "line": 172,
        "function": "dispatch",
        "class": "OC\\AppFramework\\Http\\Dispatcher",
        "type": "->",
        "args": [
          {
            "__class__": "OCA\\User_SAML\\Controller\\SAMLController"
          },
          "singleLogoutService"
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/Route/Router.php",
        "line": 298,
        "function": "main",
        "class": "OC\\AppFramework\\App",
        "type": "::",
        "args": [
          "OCA\\User_SAML\\Controller\\SAMLController",
          "singleLogoutService",
          {
            "__class__": "OC\\AppFramework\\DependencyInjection\\DIContainer"
          },
          [
            "user_saml.SAML.singleLogoutService"
          ]
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/base.php",
        "line": 1030,
        "function": "match",
        "class": "OC\\Route\\Router",
        "type": "->",
        "args": [
          "/apps/user_saml/saml/sls"
        ]
      },
      {
        "file": "/var/www/nextcloud/index.php",
        "line": 36,
        "function": "handleRequest",
        "class": "OC",
        "type": "::",
        "args": []
      }
    ],
    "File": "/var/www/nextcloud/lib/private/Log/ErrorHandler.php",
    "Line": 99,
    "CustomMessage": "--"
  },
  "id": "63c154ce1fe1d"
}