Add authextra

[konsultaner]

Did you check for unittests?

[konsultaner]

Could you fix the merge issues? I'm super Busy atm. 🙈 So sorry

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.07% :tada:

Comparison is base (a9ecb58) 90.06% compared to head (446bfa4) 90.13%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #58 +/- ## ========================================== + Coverage 90.06% 90.13% +0.07% ========================================== Files 44 44 Lines 2819 2819 ========================================== + Hits 2539 2541 +2 + Misses 280 278 -2 ``` | [Files Changed](https://app.codecov.io/gh/konsultaner/connectanum-dart/pull/58?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Richard) | Coverage Δ | | |---|---|---| | [lib/src/client.dart](https://app.codecov.io/gh/konsultaner/connectanum-dart/pull/58?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Richard#diff-bGliL3NyYy9jbGllbnQuZGFydA==) | `80.85% <100.00%> (+0.41%)` | :arrow_up: | | [lib/src/protocol/session.dart](https://app.codecov.io/gh/konsultaner/connectanum-dart/pull/58?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Richard#diff-bGliL3NyYy9wcm90b2NvbC9zZXNzaW9uLmRhcnQ=) | `85.56% <100.00%> (+0.07%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/konsultaner/connectanum-dart/pull/58/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Richard)

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