How to configure .clang-format to indent access modifiers in a class definition?

set the following in your .clang-format:

IndentWidth: 2
IndentAccessModifiers: true     #gives access specifiers their own level
AccessModifierOffset: 0       #optional; ignored when IndentAccessModifiers is true
BreakBeforeBraces: Allman     #optional; matches your brace style

With IndentAccessModifiers: true (clang-format 13+), public: is indented one level (2 spaces) and its members are indented one more level (4 spaces).

Please update your clang-format if its older than 13