add telegram auth backend support

[paskal]

Backend support for telegram auth, #707.

[coveralls]

Pull Request Test Coverage Report for Build 872936918

• 13 of 13 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 83.694%

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Totals
Change from base Build 872900139:	0.03%
Covered Lines:	5451
Relevant Lines:	6513

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💛 - Coveralls

[codecov]

Codecov Report

Merging #1022 (493d53f) into master (68aba33) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1022   +/-   ##
=======================================
  Coverage   44.18%   44.18%           
=======================================
  Files         126      126           
  Lines        2906     2906           
  Branches      653      617   -36     
=======================================
  Hits         1284     1284           
  Misses       1610     1610           
  Partials       12       12           

Impacted Files	Coverage Δ
frontend/app/common/static-store.ts	100.00% <ø> (ø)
frontend/app/common/types.ts	100.00% <ø> (ø)

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[umputun]

LGTM